Outstanding Dr's account not being paid

I was admitted to hospital on the Friday and discharged on the Sunday. I went to see my GP on the following Wednesday. They now refuse to pay the account, and I am being charged interest by the Dr, as they claim the case manager of the hospital has not updated them. I spoke to the case manager and they have indeed updated the M/A. I have queried this now quite a few times with no luck to sort it out. I have my references numbers for all the calls made to Discovery.