Nandos has no record of order and doesn't honour voucher

I am a frequent Nandos customer. I had a R50 voucher and entered it via the app while ordering. When I got to checkout I realised I'd selected the wrong store so I went back to change the store. When I got back to checkout it no longer showed the option to enter a voucher. So I just selected "pay on collection" and ordered, thinking that I'll give the voucher numbe at the store. I got an order number and it said order will be ready at 19:00. When I arrived at the store at 19:00 they said they have no record of the order in their system. However, they would put a new order through for me. When I gave them the voucher code, it said "Error" on the screen; we tried twice but no luck (and it was the last day of the voucher's validity). I won't mention here which store it was because I don't blame the store but the IT system. It shouldn't tell the customer their order has gone through to the store when it hasn't, and it shouldn't void a voucher that was entered in the app but the transaction never finalised. All in all a very frustrating experience.