It is hard to take over an account where u only have the username and password, you could send them an e-mail if you have one, posing as Blizzard and using many of the different type of scamming things, (I.E. Phishing site or just asking for the info). You could also try and transfer off the characters to a different account that you own, but you would need the name of the account that u just scammed. Also a transfer costs 25 dollars, and it is possible to reverse it if you dont ban the account, and even with it banned it is still possible to reverse, though the chance of it goes way down. So if you only have the User/pass, you are pretty much screwed if you want to keep the account, unless you can get more info.
Okey, i'll try to get some other info with a phiser then.
+Rep couse you helped me