Wizards of the Coast is responsible for all Grand Prix prizing and all prizes are paid through i-Payout. You should receive an email regarding it within a few days of the weekend. If you did not, it is likely because the information attached to your DCI # is out of date.
If you win prizes at an event, we recommend logging into your Wizards Account at accounts.wizards.com to make sure your information is up to date.
If you did not receive the prize email or are having problems receiving your prizes, we recommend contacting Wizards of the Coast Customer Support, emailing firstname.lastname@example.org or calling at 1 (800) 324-6496 (NA Only).
Learn more here: Prize Payment Announcement
You can check out additional information on the official Wizards of the Coast website: