How are you rated no 1

I underwent an operation in February this year and there was a shortfall to the anaesthetist which I paid in full and claimed back from TRA (Gap cover) who promptly repaid me . I received a letter from the yesterday claiming I owe them this amount as Bestmed had overpaid the doctor and I must now repay TRA and claim the money back from the doctor , this is surely their mistake and they should resolve this and not expect me to sort out this mess. I tried for over an hour yesterday to contact them telephonically , they just say they are busy and hang up. I went online onto their chat board and was told that this is a query and cannot be handled in the chat room and also wanted me to send them all the documentation surely this must all be on my file and on record