I had shoulder surgery 3 years ago.  I had the procedure completely pre-approved by my insurance company who paid the doctor and hospital bills after their normal discount.  A month after the operation I received a bill from a physician's assistant who helped on the operation.  I contacted my insurance company and they informed me that they do not cover the use of a physician's assistant.  I did not pre-approve the physician's assistant and had no prior knowledge that he would be involved in the operation or that my insurance company would not pay.  Am I liable?  It seems to me that there was no contract between me and the physician's assistant.
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			Thanks