Not to get off topic here and hijack your thread, but here's what happened to a friend of mine several years ago.
She had surgery on her hand. She double checked to make sure the hand surgeon was a preferred provider on her insurance list. Then she had an initial appointment, and, sure enough, it was billed through her insurance as a preferred provider, no balance billing. Seemed straight on.
The she went in for hand surgery. Immediately after surgery she went for several sessions of hand therapy. Then she gets a bill fo $60,000 not paid for by insurance~

How could that be? Surely must be some sort of mistake. The EOB said non-payment due to using an out-of-network provider. She called back her insurance co, to inform them that a mistake had been made, her doctor was definitely a preferred provider.
Oh, BTW, she made complaints to the AMA (which is a private organization, not a regulatory organization), state board of medicine, attorney general's office, the answer was the same--the doctor had acted in a legal manner and she had no recourse.
Yes, indeed, her doctor was a preferred provider. But his hand therapy clinic was not a preferred provider. He not only billed the therapy under the hand therapy clinic's provider number, he billed the surgery using the hand therapy's provider number! Surely that's fraud? No, sorry. I even called on her behalf--she's somewhat hard of hearing and English isn't her primary language. I was told that its actually legal for a provider to bill under any provider number he legally holds, its the patient's responsibility to verify if the provider is in network or not. But what can you do when the SOB has multiple provider numbers and choses the one best suited to him, without your knowledge?
They ended up working out a payment arrangement with said doctor, still owed $15,000, SOB acted like he was doing them a favor by writing the bill down then setting up a payment plan.
Since then, I make sure to get my doctor's provider number and write on all statements of financial responsibility that I will only be responsible for charges filed under that number. I've never had such problems with my doctors, but you never know. What a $hitty thing to pull on someone--even if they were just a lowely patient.

The patient, of course, is the lowest form of life in the medical world!
