If the attorney is demanding you to cease and desist from conduct which is unambiguously required by the court's orders, then that would be evidence of a violation of an act of moral turpitude, as it seeks on its face to cause an adversary to violate the "law of the case." Bus. & Prof. Code 6106, and is grounds for "disbarment or suspension." You can complain to the State Bar.
The attorney's alleged conduct could also be prosecuted by the court as contempt. But, you would have to file an affidavit of contempt and prove your case to the court.
In neither circumstances, can you get any money from the attorney's actions. So, if that's what you're after, fagetaboutit!
Re language in a letter, frankly, I wouldn't respond -- I would file a complaint with the Bar and bring an affidavit of contempt, and let the court decide if the attorney's admonition to violate the current court orders is worthy of a contempt order.
Assuming that it's as you describe, then I don't see why it would not be contemptuous. But, I'm not the judge, and I probably don't have all the facts.
If you really want to respond in writing (and I wouldn't), my response would not be strong -- it would be dismissive. E.G.: "I am in receipt of your demand letter. I shall give it the consideration that it is due. Sincerely, [yourname]"
Hope this helps.