I had a similar experience with some nurses that showed up during my daughter's birth. It was an in-network hospital, pre-approved by the insurance company. The provider that sent the out-of-network bills included a letter with word-for-word what to say to the insurance company (along the lines of "no in-network option was available to me"). I called and opened a grievance because my plan had no out-of-network coverage. Strangely, the insurance company accepted one out of two bills from the same provider. The second bill they passed through against the deductible which I was able to get reimbursed from my employers HRA. Needless to say, this year I moved back to a plan that included out-of-network benefits.