Fedhealth dysfunctional service

Did everything that Fedhealth require from it's member before my son's was admitted. Authorazition was granted but when the claims started coming in the anaesthetic claims was not paid in full. After the first follow up I was assured it was a mistake from their side and it will be rectified. Needles to say it wasn't resolved and after another couple of calls, empty promises and holding on for ages still nothing. And now I'm getting demand letters from the doctor.