Please help with Engen 1App

I am very disappointed with the service that I have received from Engen 1App, for the past three weeks I have been unable to pay for my fuel using the App. I have more than R1000 in my App account and when I scan to pay it either says QR code error or don't say anything at all. I end up using money not meant for fuel and it so inconveniencing. have made several complaints with no assistant.