Years ago, I had something similar, went to in-network hospital with my in-network doctor, and got some out of network anesthesia doctor (something I had no control over).
So they billed me ~$1K for him.
It took over a year every couple of months to phone in and fight the same bill, repeatedly..
I would have given up, which is what they want, but DW knowing the system better encouraged me to continue to fight.
Finally they wiped away the bill.
But I shouldn't have had to do all that and spend all those hours on the phone each time.