What about a humble letter, uncomplainingly explaining your situation, asking for help. If this is refused (unlikely if I were to write such a letter) you might see if the professional association would be help. Either way you'll have to be nice.

PS sometimes you can strike a case where the person who is supposed to do the work gets a huff going or something and will not help whatever. Sometimes you can ask a lawyer (? your country) to make the request on your behalf, which is likely to evoke a response.

I'm in Louisiana, US. Do you mean write a letter to my 2nd Orthodontist? I already tried to make amends with him, but they said they won't/can't take me back. I tried to see other Orthodontists local to me and the only other 2 which are nearby said no. I can't afford a lawyer right now.