Account stolen?

This would be a compromise.

I'd go over all the instructions below. You'll want to start trying to reclaim this with Billing. They may require some proof of identity, but they can tell you what you need to do at that time.

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If an account has been merged to a Battle.net, or if an email has been changed, or an authenticator added to the account (not the player's own) one of your first stops is going to be Billing. They need to get those sorted out first so the rest of the processes can continue.

Billing and Account Services
Phone Support - 1 (800) 59-BLIZZ (1 (800) 592 5499)
Live Representatives Available 7 days a week, 7am to 8pm Pacific Time
E-mail Support - [email protected]

Players in Australia should call 1-800-041-378
Players in Singapore should call 800-2549-9273
Players in Chile should call 1230-020-5554
Players in Mexico should call 001-888-578-7628
Players in Argentina should call 0800-333-0778
All other international players should call: (949) 955-0283

Now, it's very very important to figure out where the security breach occurred. If they CAN get back in, they WILL be back. That, unfortunately, you can count on.

These two stickies should prove helpful.

Computer Security Recommendations
http://forums.worldofwarcraft.com/thread.html?topicId=1778038509&sid=1

Account Compromise Info Center
http://forums.worldofwarcraft.com/thread.html?topicId=14318909866&sid=1

You may also want to look into getting an authenticator for your account. It's no substitute for good security habits, but it will help keep them out of your WoW account.

Blizzard Store
http://us.blizzard.com/store/

Mobile Authenticator
http://us.blizzard.com/support/article.xml?locale=en_US&articleId=26109

I do wish you all the very best on a speedy recovery.