VISA Reward Cards Expired

It makes no sense that AT&T VISA Reward Cards have expiration dates. The money on them was our incentive for getting AT&T, but we just realized that the cards expired a week ago -- even though checking their balances by phone reveals they still have balances on them that we cannot access. I called to ask if the expiration date could be extended, and was told no. So essentially AT&T gets to keep the money we were supposed to get as a sign-up incentive. Imagine how delighted this makes us feel as AT&T customers.