insurance help!!

Hi, I was told on Nov 18, that I was denied for gastric bypass surgery. I was never given a specific reason why. And I have yet to receive the official letter of denial. In the plan summary there is nothing stated about gastric bypass. I have asked for the plan utilization guidelines, and the company who does the precert tells me to get it from teamsters, and teamsters tells me to call medcare, the pre certs. They are acting hostile, and really do not want to talk to me, when I question them on what they based their decision on for the denial. I am getting nowhere with them, any suggestion? thanks