That's pretty common on Feral Heart, and it's pretty annoying.
Everyone has the right to play as a character from a book, movie, games, TV show, ect. and nobody has the right to claim the character as their own, or tell someone they can't play that character.
Also, I think you handled the situation in a bad way. What you should have done was just block the person right off the bat. When it comes to people like that, blocking them is the best option. Responding with more violence doesn't help the situation at all. It just makes things worse and it could get you reported.