An authenticator is on the Battle.net account that you did not add.

It is not possible to merge the progress of two or more games into one.

Instructions on linking your MLG and Blizzard accounts

Information regarding the legality of sharing an account.

What to do if you found a charge on your credit card, bank account statement, or PayPal account that you don't recognize.​​​​​​​

Troubleshooting steps for this error when installing Blizzard games

Recovering a Battle.net Account when the email address has been forgotten

How to pay in a different currency in the Battle.net Shop

Questions about the Blizzard Internship program

What to do if you cannot change the email or phone number that shows on the login screen because the field is greyed out