SPUR no more

I am very disappointed with SPUR. My wife and I go regularly to eat there and have over the years spent a considerable amount there. The issue is with their loyalty program. this is to warn customers that their loyalty vouchers are not always real. We got a voucher(the app was showing a voucher) that I checked and decided last Sunday to go for lunch based on that. When at the SPUR I checked again and gave my phone to the waiter to pay. When she came back the voucher was gone. SPUR claims that it could not be the case as there is no proof of such. Whether it was an error on my phone or an error on SPUR side, I do not know, but suffice to say that this is the last time we will be going to SPUR, as we cannot trust their loyalty programme for what it is. I have no confidence in it anymore.