There are several good suggestions but to be formal and uphold your appeal rights it does have to be in writing and via certified mail for your appeal.
Depending on your state the insurance commissioners are coming down hard on the plans for bad data on the provider websites and directories.
The plan can pay an out of network provider as in network so you can request that.
You can also contact your legislators for help. The insurance companies hate legislative complaints.
There is a difference here to make everyone aware so you know to ask the questions in the future.
The people who perform tests/x-rays etc and the people who read and interpret them can and often are separate. Both contract separately and charge separately.