High risk
020 4621 3525
AI Summary
Based on 6 community reports
This London number on the Colt Technology Services network is impersonating O2 mobile, claiming customers need to replace their SIM cards. Callers are using classic scam tactics: they can't answer basic account questions when challenged, they're pushy, and they ring back repeatedly when you hang up. The most telling report describes a caller demanding payment (taking £1 from the bank as a supposed "deposit"), promising free tablets and cheaper contracts that don't materialise. Don't engage with these calls. O2 will never ring you out of the blue demanding SIM replacements or taking money upfront. If you're genuinely concerned about your O2 account, contact O2 directly using the number on your bill or their official website. Block this number immediately.
Written automatically by AI from the community reports on this page. It does not set the spam score, and it can make mistakes, so read the reports below as well.
Pattern detected: Broadband or telecoms scam
Several community reports about this number describe the same experience.
Multiple reports mention a supposed problem with a broadband or phone service, and references to O2. This reported pattern suggests the displayed number may be used in a telecoms impersonation attempt.
Based on screened community reports only. Caller ID can be spoofed, so reports may describe misuse of the displayed number rather than the registered number owner.
Common details reported
Details that appear in two or more community reports about this number.
- Reported scam type
- Broadband or telecoms scam
- Claimed organisation
- O2
- Recommended action
- Contact your provider directly using the number on a recent bill before acting on any warning.
6 moderated reports
Every report on this page was screened automatically and then approved by a moderator before being published and counted towards the score. How moderation works
Cumulative spam score based on all reports up to each month. Higher percentage means higher reported scam risk. Cumulative spam score based on all reports up to each week. Higher percentage means higher reported scam risk. Cumulative spam score based on all reports up to each day. Higher percentage means higher reported scam risk.
Most helpful reports
6 totalSubmitted by users and shown as written, so wording and spelling are their own. Each report is screened and approved by the CallerCheck Moderation Team before it appears.
Got a call from someone saying they were O2 but they couldn't tell me simple info about my account so it was most likely a scam.
Said they were from 02. Beware, you dont know what your signing up for
Said they were from O2, but obviously weren't. The typical Indian (are there any honest people left there?) scam call centre.
Female said she was from O2, a mobile provider, saying I needed to replace my SIM. She rang back when I ended the call, angrily asking why I had hung up, and then called again a third time.
Very pushy- I hung up and she rang back asking why I hung up in a rude way -
Said that they're from O2 and need to send two new SIM cards (for my 2 lines) by DHL, arriving tomorrow. Took £1 from my bank which they said will come off the next bill. Will get cheaper contract. Will get a free Samsung tablet. All lies!
Share Your Experience
Help others by reporting what happened
How this page was checked
This profile is built from community reports, lookup activity and CallerCheck risk signals. It is not written by hand for this number, so the details below show who checks what and when it last changed. The risk score is based on community reports about calls and texts from this displayed number. It is not based on official records of who owns the number.
- Reports moderated by
- CallerCheck Moderation Team
- Safety guidance reviewed by
- CallerCheck Editorial Team
- AI summary
- Generated from approved community reports only
- Last report received
- 11 Mar 2026
- Last reviewed
- 25 Feb 2026
- AI summary last generated
- 02 Sep 2026
- Last materially updated
- 02 Sep 2026
What do these dates mean?
Report and lookup dates come from user activity. Review dates show when CallerCheck last checked reports, safety guidance, or risk signals. We use “last materially updated” only for meaningful page changes, not cosmetic changes.
- First seen:
- when this number first appeared on CallerCheck, through its first lookup or report.
- Last report received:
- the most recent approved community report for this number.
- Last lookup:
- the most recent time a user searched for this number.
- AI summary last generated:
- when the AI summary on this page was last rewritten from the approved community reports.
- Last reviewed:
- the most recent human moderation or editorial review, where available.
- Last materially updated:
- the most recent meaningful change to this page: a new approved report, a risk score change, an AI summary regeneration, a moderation action, or a claim or dispute change. It does not move for cosmetic changes.
Sources and safety guidance
- Community reports about this number, screened before they are published or counted. How moderation works
- Ofcom numbering allocation data for the network this range belongs to
- Safety guidance aligned with UK scam-reporting advice, such as Action Fraud guidance, forwarding spam texts to 7726, and the 159 banking helpline where relevant. Where to report a nuisance call
Important limits
Caller ID can be spoofed, so a high risk rating means people have reported suspicious activity involving this displayed number. It does not prove that the registered owner of the number made the call or text. Community reports describe individual experiences and are not official confirmation of a scam. How caller ID spoofing works.
Own or manage this number? If this number belongs to you or your organisation, you can claim or dispute this profile. We review claims, check supporting information, and may update the page if reports appear to involve spoofing, mistaken identity, or outdated information. Claim or dispute this number
About 020 4621 3525
What type of number is 020 4621 3525?
The phone number 020 4621 3525 (also written as +44 20 4621 3525) is a UK landline number originating from the London area in Greater London . Calls to this number are charged at standard UK landline rates, usually included in call packages.
Is 020 4621 3525 safe to answer?
Based on 6 community reports, this number has been frequently reported as spam or a potential scam. The current risk score is 100% with 6 reports marking it as spam .
Exercise extreme caution if you receive a call from this number. Do not share personal or financial information.
What this data can and cannot tell you
Everything on this page comes from reports submitted by members of the public about calls and texts that showed this number. Caller ID can be spoofed, so the person contacting you may not be the genuine holder of the number, and a legitimate number can be misused. Before paying anything or acting on a message, check the claim with the organisation involved using contact details from its official website or letters, never the ones in the message itself.
More on nuisance calls
Safety score
6 reportsHow this score was worked out
Each report rates the number as safe, unknown, suspicious or spam. The score blends those ratings, giving more weight to the more serious ones, and a number with only a few reports is held closer to neutral until more arrive. Feedback votes on reports can also influence it slightly. Scores of 70% and above count as high risk, 40% to 69% as medium, and below 40% as low. More about spam scores
Why this number is rated High Risk
This number is rated High Risk because 6 of 6 reports classify it as spam or suspicious, and several reports describe the same broadband or telecoms scam. No reports identify the number as safe or expected.
Ratings reflect screened community reports, not official records. How the spam score works.
Confidence: High
Based on 6 community reports with repeated matching details. Confidence describes how much report evidence sits behind this page, and is separate from the spam score.
Caller ID can be spoofed, so reports may describe misuse of the displayed number rather than the registered number owner.
Details
- Tel Number
- 020 4621 3525
- Country
- 🇬🇧 United Kingdom
- Network
- Colt Technology Services
- Area
- London
- Type
- Geographic
- Coverage
- London and the surrounding area
- Cost to call
- Standard landline rate
- First Seen
- 17 Feb 2026
Network shows the operator this number range is allocated to in Ofcom numbering data, so the caller may be on a different network if the number was moved or spoofed. First Seen is the date this number first appeared on CallerCheck.
What To Do Now
Steps that fit the broadband or telecoms scam pattern reporters describe.
-
1
Do not share personal or payment details
Do not give personal information, card details or security codes to an unexpected caller or message.
-
2
Verify independently
If the caller claimed to be an organisation, find its official contact details yourself and check the claim directly.
-
3
Block and report the number
Stop further contact from 020 4621 3525 and forward scam texts to 7726. How to block a number on any phone.
Already paid or shared bank details? Call your bank straight away using the number on the back of your card, or dial 159 to be connected to your bank securely.
Call Types
Breakdown of reported call reasons. Larger segments and bars represent a bigger share of reports.
Location
London, United Kingdom
This number originates from the London area code region. The map shows the general geographic area, not an exact location.
Protection Guides
How to Block This Number
Clear instructions for iPhone, Android, and landlines
Caller ID Spoofing
Scammers can make any number appear on your phone, including your bank's real one. How spoofing works, how to spot it, and what to do if your own number is being used.
HMRC Tax Scam Calls
How fraudsters pretend to be HMRC and threaten arrest over fake tax debts, or offer bogus refunds to steal your details. How to spot them and what to do.
Bank Impersonation Calls
How fraudsters pose as your bank's fraud team, spoof their number, and trick you into moving money. What to look out for and what to do.
Is this your number?
Claim or dispute this profile
We'll verify ownership via callback or documentation
We review claims carefully and may keep warnings visible where community reports still indicate risk.