Used last money for transport to go buy food with voucher, ended up with no money and no food

I got some Nando's vouchers using my vodabucks on the Vodacom app, I live about 5km from the nearest Nando's. On Saturday the 20th May we only had a little bit of money so we decided to use the money for a bolt to go and get Nando's because it would be enough for the 4 of us (me, my husband and my 2kids). We arrived at Nando's and I placed my order but as soon as I started giving the cashier my voucher code she said I should wait just a moment, she then went and got the manager. The manager then told me that their system is offline and they can only accept cash at the moment. So then we had to take the bolt back home. No money left and no food. We were so disappointed. Can someone please explain to me why their system has to be offline during business hours.