Redemption is very strict. You can never change your order once placed, even if it is a mistake.
However, when they are the ones who send you a wrong item, it will take at least 10 (ten) phone calls and a wait of not less than 6-10 (six to ten) weeks before they can decide what to do with it.
Really, Flex Perks. You can do better than this. Do not make your rewards into a living hell punishment. It is your fault. Fix it speedily - at least as fast as you apply your numerous penalties to your unfortunate customers.