An instore voucher query

I bought an instore restaurant voucher from them, which got declined in 3 different stores. After informing them about the voucher, they promised to resolve the issue, then they issued me the same voucher code, which declined again. Again I informed them and even sent them the receipt from the store, they again promised to sort this out. A few days later I was the one who contacted them, and they told me that the issue has not been sorted and they are sorry for the inconvenience. I waited a few days and then contacted them again. Well guess what, the person I spoke to had no idea what I was talking about. I had to resent the receipt from the store and also explain my query all over again. Now am waiting again, and I really hope they sort out the issue and contact me before I contact them, because wow! Am really tired.