Well, giving warnings and warnings and again, warnings, never helps. I've done this and it was a mess. Now I make it clear that my rules need to be respected, if not, they're out. If the know 2 max 3 'strikes' get them permanently banned, users tend to behave. And long time members can be banned (and are on my forums) no matter if they have 20k posts or 20 million. I don't care, if you can't respect few guidelines, then we don't need you
Congratulations for the ban, keep an eye on the guy, he'll probably re-try to join. Keep on banning each account he makes and he'll eventually lose interest.