You are responsible. It is YOUR medical insurance--it is your obligation, not the doctor's, to make sure you have the coverage for the procedure that you think you do. And you are responsible to pay--either through your insurance or, if insurance does not cover, out of pocket--the costs for the procedures you have done or medical care you receive. So if your referal had expired, it is unfortunately your responsibility, and therefore your responsibility to pay for the procedure since the insurance will not.