Forgotten Email
Nexon accounts are tied to your email address. When you originally signed up for the account, you entered an email address and received a Nexon Passport ID after you confirmed your email address. You used that ID and your password to enter the game thereafter and it's possible that you forgot which email you used to create an account, especially if it's been a few years. After Nexon deactivates your account, you will need to be able to access your email in order to reactivate it. You cannot change the email associated with the account without submitting a Nexon customer support ticket. Don't forget to give an email in your complaint at which they can reach you or they will respond to your old email.
Different Country
"Mabinogi" for U.S. servers prefers U.S. IP addresses although you can start an account from another country. If you move out of the country in which you started an account and attempt to log in, Nexon may register the login as a hacking attempt and will shut the account down. Contact Nexon and explain about the move to reactivate the account.
New Internet Provider
If you recently switched from one Internet provider to another or even if you upgraded your Internet connection from the same provider, you may have another IP address. When you try logging into "Mabinogi," Nexon may register the new IP address as a hacking attempt and you will have to contact Nexon customer service to resolve the problem. You can only contact Nexon customer service via its online form.
Different Location
Whenever you use a different IP address than the one with which you originally signed up for your Nexon account, you may experience difficulty reactivating an account. While going to a friend's house or to a public provider of Internet to play will not always result in deactivation of your account, it may contribute to your reactivation problem should you attempt to log in for the first time after deactivation at another location.