Gukai,

The SQUARE ENIX MEMBERS site is a completely separate service from the SQUARE ENIX Account Management system, even though it uses the account management system. The SQUARE ENIX MEMBERS site being down do to unauthorized access will not keep you from logging into the SQUARE ENIX Account Management system itself to manage whatever services you wish to manage.

The SQUARE ENIX Account Management system can be reached directly at:
[SQUARE ENIX Account Management System