[Parliament]

Nothing I think you can really do, the youtube copyright system is broken along with the fact that it has a long ass form that needs legal information and more. I'm pretty sure the user you've claimed can see your legal information as well when you send it. Could attempt to contact the user and threaten them into removing it, which I doubt they'll do. I'd say put watermarks in your videos in the future with your channel link so this can't happen again.