Contact Customer Support using the In-Game options to do so. If you are alliance on one of the Horde-restricted transfer realms that they updated 2 hours ago in their sticky post.
You might be able to get your transfers reversed in this specific situation due to the circumstances. Seemingly, transfers to these servers for alliance were not supposed to be activated at all and some people who jumped on them at first open inadvertently were allowed through - thus, creating the problem.