You can't join because SOE decided to make that channel (as all class channels) server-only (just ask another wizard for the new worlwide channel) and you can't leave because that's another game bug that has been there since launch.
If you want to get rid of the channel exit the game, open the appropriate
server_character_eq2_uisettings.xml in your eq2 folder in a text editor, search for
guk.wizards and delete that entire line. Save and restart the game. Maybe make a copy of the file first in case you mess up.
