Voucher redundant

I was at Shoprite Klapmuts today at about 10H30. I have a 1Voucher voucher and wanted to redeem it. I asked at the help desk how it works and the manager asked one of the staff to assist us. She punched the voucher nr the money market screen a few times. She said sorry it is not working. We left to try at another place, as this is new to me and I was not sure how it works. When I got home and tried to use the voucher on the 1ForYou app, it said that the voucher has been used and is now invalid. So my money on the voucher is gone and the only place we were at was Shoprite. I tried phoning the store to talk to the manager and find out we're my money is, but they do not answer the phone.