I've seen some people that named their character the same as few characters as mine.
For example, Daku and I've seen the username Darkmist, but I didn't consider them 'stealing' unless they went up to me. I wasn't on the characters with those names too.
I rarely find names like my characters, and I don't find any stealers, actual name stealers.
But if someone is taking a name on purpose and steals the character itself, then that's just plain rude and uncreative.
I always admire creativity when I see it everyday, but name stealing isn't creative, nor is character stealing.
I'm sorry this happened to you to be honest, but there's always the block button if they try to argue with you, isn't there? :3