When you buy credits, your credit balance should update after a few minutes. When in doubt, you can log out of your account then log back in. This will refresh your credit balance.
If you already did this, and your credits are still missing, please make sure the transaction really took place. When you make a purchase, you receive a payment receipt via email. If you have this receipt and not the corresponding credits, please contact our support department via the link below. Make sure you send us a copy of your purchase receipt so we can help you quickly.