rhianonm:No, he had a letter asking us to call the Natwest Birmingham Collections Centre, which he did. That's I guess why he assumed he has spoken to Natwest themselves.
OK, Natwest sent a letter, that's reasonable but possibly precipitate, however it was a student account and perhaps NatWest saw no evidence of the account being sufficiently funded.
Sorry I digress, they sent a letter asking you to phone, you phoned and they made some crude suggestions. Do you have a record of that call? You do not need to subject yourself to phone contact if you don't want to. Up to you but you are entitled to insist on mail or email if you want and you cooperate (Banking Codes say so)
I suggest you take urgent steps to obtain the recordings of the calls you made. You need to make a £10 Subject Access Request of Natwest. Request all your data but specifically the call recordings. If no recording it never took place, rewind and start the process again, although if your phone bill shows a call was made you can have some fun with NatWest data protection.
You can do the SAR in parallel to the complaint, though personally I like to have the SAR data to inform the complaint and assess any response.