Check your email again! The one you used to register the game, you will have a new email from Square Enix with a new code, the code you are trying to use is the Early Access one, you now need to input the real game code.
The emails are sent from:
webhelp.v4@digitalriver.com
Subject: Square-Enix, Inc. - Product Now Available (Order #XXXXXXXXXXX) <--- your actual order number
This is from an US account btw, dunno about EU.
I received mine on the SPAM folder dunno why, check it out and you will be ready to go in no time.
Hope it helps =)