Mafia can be used as last name. Doesn't looks like impersonation to be fair. It's a well known gaming name and can be used the way he did. For example, if he had used something like "Mafia.." or "Mafia1", that could be impersonation. Many of us knows, Mafia is a part of VU so he will be using tag whenever he will play, not a big deal.
Just shared my opinion as I found a little misunderstanding from your side, maybe.
