How to resolve mistakes claiming a CoD key on the wrong Battle.net account
Troubleshooting problems with the Battle.net friends list
What to do if you receive an error that your code is already claimed in your account.
What to do if any settings you change do not save
How to obtain error logs for Blizzard games
Information about this error when redeeming a key in your account
What to do if you have trouble with the captcha
How to install a Blizzard game you already own on a different computer
Troubleshooting step for connection-related problems on Windows.