People are morons. Sorry for what happened to you, but trolls are trolls because they think they can get away with it.
Warnings should be issued before a ban, but that's at the discretion of the admin (most of which should not have that power).
When you defend yourself against these trolls, just block. Yes, it's a major offense, but sometimes admins are complete idiots, and do stupid shit. Some even think it's a license to troll.