You said "the insurance company came back and said..." I am a parent who has had run ins with insurance payments and have learned to put it in writing. Send a certified letter to the insurance company as an appeal. Call to get the address for sending in an appeal. Include a copy of the EOB and print outs of the insurance company's provider search showing that the provider is covered by the network.

If there is a written response still denying the claim, then contact the government agency responsible for appeals.

I'm just the family's payer of medical bills, but I've had a few declines that have been reversed. One was a $20,000 bill so that was scary! What I have learned is insurance companies don't seem to take things seriously until you put it in writing. Don't worry about a second EOB,either. Once you put in an appeal, it's like having a dispute on a credit card charge: you have time to work out whether or not you have to pay the bill.