Greenmangaming should of given you an NA code if you placed an order in NA. Their service is region specific. Log in on your GMG account and check the region of the game, what does it say? Do a manual search for Final Fantasy XIV. Does it say the title without (NA)?

The e-mail sent to me was said:
Please go here - http://preorder.eu.finalfantasyxiv.com/us - to redeem the pre-order code you received when you purchased the game.

What did yours say?