Is my insurance overcharging me?

Before my jaw surgery my insurance conducted a pre-approval investigation and it was deemed that it was medically necessary and they would cover 100% of the costs. This was done in full knowledge that my surgeon was the one performing the surgery. However, my surgeon was considered an out-of-network doctor. I got the surgery done and now my insurance will not cover the cost of the operation. Am I correct in that despite the surgeons out-of-network status I had a prior authorization number stating they would cover the costs with this surgeon? or am I wrong and am responsible for the costs despite no one alerting me of their non affiliation or alerting me that I would have to cover all the costs?