Pre-authorization vs approval???

I am SOOOOOOO  confused now!  My surgeon's office says I have been "approved".  However my insurance company says bariatric surgery is not covered and a pre-authorization does not mean insurance will pay. Can anyone explain this to me??  I do NOT understand!  Should I go ahead with it?  I have a date and everything. 

that doesnt make any sense but... if youre going to an in network provider and they perform a procedure that needs prior auth and they dont get it they are liable as long as you dont sign a waiver on the day of the surgery, pay attention to everything you sign do not sign a waiver and you should verify all of this with youre insurance company also tell them you want a copy of the aproval letter. goodluck