You aren't running Innerspace or anything like that, right? Recruit-a-friend shouldnt get you banned, since you can't get past level 20 with it anyways. Maybe someone saw you and reported you as a bot, but the GM should have been able to check you are in fact not botting.

Thats one thing I hate about WoW, for no reason at all you can get banned and there is sometimes almost nothing you can do to fight it.