Basically if you get banned x number of times within a month (I think it's 30) then you get blanket banned from all servers. As for why, I don't know
Maybe contact the server admins of some of the servers you've been banned from to work out why?
If it's genuinely a mistake (although being banned 30 times implies something is wrong) then you can probably apply to have it revoked if you do get a blanket ban.