You may need to contact the Square Enix Support Center so they can check if the registration codes were added to the right account and were not used as a new account. Please make sure that these steps were followed when you created the new Square Enix account.

(1) Log into the Square Enix Account Management System using the Square Enix Account that is tied to the service account (PlayOnline ID) you are playing on.
(2) Choose “Select Service” from the left menu and select “PlayOnline / FINAL FANTASY XI.”
(3) Click on the “Add a service account” button and enter your expansion software registration code.
(4) Follow the onscreen instructions and select the service account (PlayOnline ID) you wish to register your registration code.
(5) Carefully review the information displayed in the confirmation window and complete the registration.