Coast Dental Services review: unethical billing practices

I had a root canal done by these people. They gave me an estimate of coverage and told me that my part would be $700.00. I paid the amount and after the service I get a letter from the insurance company saying that they denied part of the payment because the dentist did two procedures on the same day that he should have made two separate appointments for, this was not told to me by the dentist. I now am being billed for another $719.00. This is something I should have known HOW? I even asked the dental office if they could do something and of course they said NO. I am calling and writing to everyone I can find who might be able to help to stop these awful practices. Taking money from people who are working in good faith with these characters should not be allowed.