Overcharged, zero feedback

I placed an order online and received it within half an hour, which was excellent. However, when looking at my invoice, I had been overcharged by approximately R105. Instead of honoring the app price of 2 for R79, they charged me buy 2 at R79 and get 20% discount. I have complained a total of 5 times - twice by telephone, and once via the app and twice via email. With absolutely ZERO response. Checkers 60Sixty is clearly making too much money to care about customer complaints.