authorization declined after surgery, poor service

i had surgery on the 6th of August, and discovery approved part of the surgeries. now after approval they decided to reject everything. i called them on Friday was on the phone for 40 minutes. there case manager will sort it out. i called again today and they said its been rejected because i didnt get prior approval. but i have an authorization umber. what is the story with discovery? how do you issue authorization numbers and now reject everything. im tired of being on hold and nothing get resolved