Just a question (???huge bill???)......

 Hello Everyone.  I have read several post throughout the boards that a person has received a huge bill from the hospital after surgery even with insurance approval. How is this possible if you have approval from insurance company and a max out of pocket? I'm starting to wonder if I need to call my insurance company myself and confirm my responsibility. Is something not being mentioned when peeps are saying they got a huge bill???

Thanks!
Auburn