There's always a clause the insurance company uses before you are transferred to a rep that says "Benefits are not a guarantee of payment and are based on coverage at the time of service"
Did you get the first rep's name? Sometimes that will help you out. If you didn't then there really is nothing you can do. Double check your provider guide to see if the hospital was listed, call the hospital and check with them to see if they were a participating facility AT the time of your surgery, if they just recently dropped participation you might have a good shot of appeal since you verified they were in network before your surgery. Many of these can be appealed you just have to keep trying, you have a better shot of an appeal than the hospital so don't rely on them to help you aside from giving you information you might need. TECHNICALLY since all you had was a verbal, and if they were not listed in your provider guide, the carrier can deny or pay out of network. It's always much better if you get that information in writing next time, and look at your provider guide and of course make sure you have updated network guides. If that hospital WAS listed in your book but they went NON par before the next publication, that is grounds for an appeal. Good luck.