Out of Pocket not refunded

I have been going to the same dentist for years. When she went out of network, I still decided to stick with her because I liked their service. Meanwhile, the insurance provider encouraged me to consult an in network dentist last year for a dental filling. When the filling came off, this year, I went to my old provider who already had my X-rays. But she said she had to charge the whole payment $300 for the filling because she was not sure if the insurance would cover it every year. I called the insurance company and they said they would cover it but wouldn’t email me a copy.

The dentist again reassured me that this insurance provider was fine and played the fool with me in her office. But the receptionist pretended to be “mad” that the insurance ws not paying them well. She was rude. I was scheduled for the next appointment for the final filling.

For the last filling, the office charged me full payment again, $300. I was not told about this before treatment. I was shocked. This was not a tooth that was touched by any other dentist. So this was uncalled for.

Now the first payment was processed by the insurance provider. And the second one too. The dentist hasn’t refunded me anything out of $600.

I sent them repeated emails requesting for the refund and offered to submit the claims from my end. But they wouldn’t give me the dentist’s information to file the claim. What do I do? Let it go? Let her keep $600?