I've tried to use the $50 GC's from back when I had made use of the Amex Plat reimbursement for them. I had to call in to use them, tell them how much the GC's had on them (it seemed they had no way of checking?) and after two weeks or so, got the receipt in the mail. Actually, it was multiple receipts (like 10, spread over several days). As if it took many attempts for it to take. But all good in the end. Try calling.