Doctor office paid Twice? Illegal?

I went to the doctor and my insurance had changed. They are now out of network. My insurance will pay for 60% of the bill and my copays didn't change. I went in and a newbie at the office told me (after he spoke to a nurse NOT the buisness office) said I would have to pay upfront and then they would also bill my insurance and when they paid they would credit my account. My insurance company said it is illegal to do that. They said you can bill twice for the same patient and the same service regardless if it's a credit to my account. In the mean time I'm out of my medication and in pain (I have nueropathy). Is that illegal?