This happened to me... My email password was the same as my B.Net password, I got hacked on B.Net, and they used my email(same password) to move all of my wow accounts and my Starcraft account to there email address.
Ring Blizzard, tell them what has happened, they will ask you when you last played ect. They may ask for ID, or cd keys, however they didn't for me. They just checked the IP jump.
Edit: also make sure you tell them you remade your b.net to make sure you haven't just forgotten your password.