Hi Kvana
When I did this I had to go through the code entry process three times the screens on the SE Account management website are not very clear and it seems as if it has taken your code but it has not actually applied it to the account.
Login to your SE Account and do the following again
1. Click Select Service
2. Click PlayOnline/Final Fantasy XI
3. Click Add a Service Account
4. Enter the redemption code <-- if after you enter your code here again it still accepts it then your previous attempts did not fully get completed. If it rejects your code here, you'll have to play with the SE GMs here....
5. Select the account you want to apply it to (If you have more than one FFXI account)
6. Select the character you want to give the beret to. Keep in mind it will only go to one of your characters, so choose wisely!
7. Completely log out of the game and play online, wait about 5 to 10 minutes, log back in and try to get your hat.
The steps 5 and 6 are really weird this is what tripped me up is I stopped after the select account portion the method to go on to select the actual character the item goes to does not seem obvious.