in hospital accounts not paid in full

I went for a shoulder operation and was admitted to hospital for two days. had authorization for the entire operation. Yesterday 2023-09-28 i received a bill from the one Dr stating the medical aid did not pay the bill in full. According to me IN-HOSPITAL should be covered in FULL. I need this account settled. Approval was given for the operation so why would GEMS not pay all the accounts for the operation. This is really unacceptable.