I don't think it's possible, since it's not really specified in the rules that you can't name your server in a specific way. Anyway, I guess that the name you made for your own server is protected by copyright law. I'm not really into laws and stuff, but if you wan't to sue them it's gonna be awfully difficult to prove that you came up with that name first anyway. So as for now, I guess you just have to wait for the other server owner to get bored of this nonsense and stop hosting.