You had to play before November 20th, and you were supposed to get an email. But since the email failed over 20,000 people, Microsoft is now sending the code via Xbox Live. You should get it in a message this week if you met all prequistes. Live anywhere but Europe, played before November 20th, and over 17.
Xbox GT: AlchemicSpartan Pokemon Black: Dizzy - 3826 5358 7980