A digital artist is pressuring me for a purchase

Location: Colorado

On October 27th, I received an email from a digital artist(now know as hda-harassing digital artist) saying that they created some art for my story I posted on fanfiction.nett. Thing is, I never commissioned any art from them. Hda did talk about a concept that I did talk about with only 2 other digital artists, one I refused multiple times but has a different username than the one currently harassing me and the other I am working with (who has been an amazing artist to work with). I have refused Hda who emailed me many times. They emailed me some line art but it has stayed strictly in the emails. During the many emails, I did give a little and asked hypothetically what it would cost if I did purchase the art. They replied $1200 with $500 installments. I will be honest and say that I freaked out and started cussing my refusal. Hda kept pushing while I kept refusing. During this time I did call them a monster for pushing this unwanted commission on me. The reason I called Hda a monster is because this fanfiction is my way of processing my grief and other related emotions. I watched my uncle wither away and die from a rare form of alzheimers, a close friend died, my best friend of 15 years died, and my rescue dog died, all in a 6 month period. Because I was using this story to process my emotions I am very protective of it, thus my blow up at Hda. They won't stop and have threatened legal action against me. Hda states that they have talked to their lawyer but is giving me a last chance to pay. There is no contract between us. Their supposed proof of our conversation about the commission is connected to an account that is gone.

My question is should I be worried if Hda sues? If they do should I counter sue for their harassment? I am out of my depth here and don't know what to do.