OP, did you purchase this for yourself, or for a friend? If you purchased it for yourself, the item will be delivered to the character you chose before checkout via Moogle Mail. If you purchased it for a friend (Gift a Friend option), then the page should have processed your card information before loading up a new page with the 20-character gift code present.

If the option was the latter, you will need to contact SE’s Support to have them either refund you (so that you can attempt to make the purchase again), or generate the gift code for you (if that is within their power to do so).