Covid testing denied- and was told okay by customer service.

I called customer service and was told it was okay to get a covid test where I had been able to find an appointment for my son. Not much available at the time.  Also called his doctor and asked to confirm I didn't need a referral.  Today I received a letter that my claim was denied because out of network?  How do I go about getting this covered?  Especially frustrated because I called to confirm both doctor and insurance to make sure it was okay.  Doctor would see me in office anyway with him.