Possible course of action:
Call the insurance company and ask them for help. They may have nurse navigators who can steer you to a really good doctor/facility to help your dad. I had Keystone Blue Cross for years and their nurses and customer service staff were really, really helpful. Mayo IS great, but there are other good places, too.
Kudos to you: You must be a wonderful person to help your dad like this! Good for you!!! Keep your chin up 🙂 Good luck. Keep us posted.