All you need to do is to send an email to feedback@spong.com with the subject: "Oi, SPOnG, inFamous T-Shirt, Now!" in it. You can also send a tweet to spongdotcom with the same message, we'll need an email address obviously.
I think everyone who failed to follow the instructions e.g. posted in comments/forum(unless thats what was meant by tweet) and/or didn't say "Oi, SPOnG, inFamous T-Shirt, Now!" (as I noticed quiet a few just said "please send me the code" shouldn't get a code