your account name is an email address like john123 @ something.com .....it would be the email you entered when you signed up and yes you do need to include the @whatever.com
IF you used an ncsoft.com email to sign up then you should use that.
Try using an email address you have besides the ncsoft one,
also remember you will need to put in your characters FULL name in the security question (so if you character is joe smoe, you must type in joe smoe not just joe).
where is the 'all you can eat' cookie bar?