> I’m not confident that I could remain civil when talking to the person who inflicted this on me without my permission or knowledge.

I'm not sure how long anyone can last in business if this is their response to receiving a kind-of-threat of a lawsuit. I get that it may be a hassle but businesses get these kind of garbage threats frequently and often can be ignored unless and until they actually file something. If the threat is BS then its certainly wrong for them to waste your time but being so mad you can't even speak to them seems a bit much.