I am so sorry you are having to deal with parents like this. I just recently had my first experience similar to you and it was horrible!
I spoke to them over the phone and in person. I wanted very little said over text or email for two reasons....1.tone is lost over text and misinterpretation happens and 2. I didn't want her to save any of my emails/texts
I have the same thing in my contract as playfelt and when I said I was terming due to that she started asking me how she was being detrimental to my well being....oh where to start?? lol. It was very hard to stay professional with her! I eventually just had to tell her that we would have to agree to disagree. I defended myself against factual things but when it came to explaining why I thought she was disrespectful towards me we had to stop talking about it. I felt one way about her attitude and she felt another way and there was no changing either of our minds about how and what happened.
They are likely mad that they are loosing a great provider and they know it! Good riddance!!