Under "Your Account" should be where your purchase history, etc is. Hit that Download link
I already unlocked it as soon as I purchased mine I think but there should be a button there instead that says download or unlock or something of that nature. Once you press it though and you activate the key that's provided they will definitely be planning to charge you and refund will not be available.
Take that activation key from the SE store to the site highlighted.
At that point they will ask you to log in, and from there will ask you to enter in the code from SE's site/the email. I think they also ask you which type of code you are entering in (PS3, PS4 or PC/MAC)....it could be automatic too
Once entered in correctly they will display your EA code to put into the Mog Station or PSN even showing on the side which code it is. Now copy down that code as this is the one you'll be using to get EA, the bonus items, etc.