sorry if this has already been covered, but my pet code isn't working. i buy it, copy and paste it to the redemption page and it says already claimed. so i go check in game. nothing in the mailbox or the pet tab. its also worth noting that i just upgraded from the starter account, and bought the pet (lil xt) about 2-3 hours after upgrading.
When you clicked the Redeem Now button, you redeemed the code on to your account. The pet most likely will not show up until your account has fully processed as a full account...aka when your bank actually sends the funds to Blizzard for the account.