Unless you go into the chatroom and start spamming up the room (for example, constantly trying to throw everyone off the topic they're on, advertising other places, flaming/insulting people, typing nothing but one word over and over, etc), then you should have been warned before you were banned. Someone should really talk to shuten, though... or if not him, Zephy. FFChat ops are meant to be respectful, no matter how powerhungry they are. They should never ban without a valid reason, as in #eoff, they are representing Eyes on Final Fantasy. I think I talked to Zephy (it was someone, I think it was him...) about this a long time ago and he agrees.

EDIT: Of course, if you were banned from another room in FFChat, such as the chatroom for FFOnline or FFLegend, then you've probably dug your own grave. All of these chatrooms are on the same server, and the server ops (FFChat staff such as shuten) can give server-wide bans if you disobey the rules enough.