voucher invalid

absa has a accept challenge that they offer from time to time i did the challenge and got a voucher chose the where i want to use the voucher now i wanted to use the voucher it does not work its ****en invalid really now i looked like a ass using it at nandos it just kept saying invalid absa is hopeless really how can they embarrass me like this its **** imagine i go there i want a full apology from them how can the voucher that expires next year be invalid what the ****