Someone banned me! What can I do?

What you need to understand is that channel ops may kick or ban an individual for any reason or for no reason at all.

The most you can do is to ask a channel op to unban you. To do that, type /who #channel or /names #channel and /msg or /query one of the channel ops (their nick will be prefixed by an @ symbol), and politely ask them to unban you.

Note that if the channel is mode +s (secret), or the ops are usermode +i (invisible), you will not see their names displayed. In this case, you may choose to ask a friend to join and find out the names of the ops for you. However, that may result in both you and your friend being banned. #help cannot help to resolve these personal channel matters.

If the channel is registered, you have access there, and the ban level is lower than your access level, you can unban yourself with: /msg X unban #channel yournick