You were likely banned for spam. If it weren't enough, you also admit that you have had multiple accounts?
The only plausible thing to infer is that you were spamming the forum with all of your accounts and thus have already faced bans previously. Since you did not learn your lesson, you were punished for it. Permanently.
When you're posting every 2 minutes, then there's a problem. (6 posts within 12 minutes, seen on knowhow's post history
[Archive]) When you were able to post 20 posts in an hour, there's a problem.
Care to list the alts for us, by the way?