Discovery Bank Cashback Rip-off!

This is my last attempt to understand why we're ********** by Discovery Bank. They offer a service and make you buy all sorts of healthy foods with a promise of a cash back only not to pay you back. Since March I've kept every receipt of foods I bought and when I get the cashback it's not equal to what is on the app at the time of purchase. I've calculated my spend for every month, and the call centre does not help because one gets transferred around and when you log a query feedback takes longer and at times is non existent. It's truly disappointing...but based on these reviews, I'm not surprised. Unless someone sorts this out for me, I'm joining other customers at the exit door.