A while ago I had someone come to me and attack me the same way, I actually posted an advice post about it too. They claimed I didn't do their commission and said I was someone I wasn't. I repeatedly asked for proof and they never showed it. They also threatened posting me here and spammed all my commenters in the journal I had posted slots in.

Eventually he just... vanished. I know it's not much help but it may be the same guy.