Denied AFTER Approval Code!

To laugh or cry?!! My docs office got pre-approval for surgery in-network. My insurance broker told me that my new health plan with Humana includes Bariatric Surgery. I went ahead with it and got Sleeved a month ago. Doc did not require anything up front and insurance was approved. Received Claims last week from Humana that all charges associated with this have been denied due to lack of coverage of Bariatric Services. Just wrote an appeal - ahem....long, detailed with pre approval code and my anger all displayed in letter. What gives? Could they really deny this?? I am infuriated and told them so. I should be recovering and focusing on my health but stress does not even begin to describe what I am going through with them. Any thoughts or advice so appreciated.