United Utilities calls

"Said they were calling from United Utilities to renew the direct debit for insurance. then said the insurance company was linked to United Utilities. Wanted my bank details. They had my sort code but not the account number. I declined to provide it saying I wanted details by letter. Was transferred to a 'manager'. I continued to decline and asked for written details. Call terminated after the manager agreed to write. Further call 5 minutes later from a 'higher manager' who had listened in to the earlier call. Paperwork could not be sent without my account number. Eventually, he became very argumentative so I terminated the call."