PNP Thabong shopping center pathetic service

I have used my smart shopper card, and I won a promotion that 25% off white star maize meal 2.5kg, 5kg or 10 kg, I went to Thabong shopping center in Sebokeng to claim my discount and decided to take 5kg and when I got to the till the supervisor was forcing me to take 10kg as their machine does not allow them to claim for 5kg and I refused as I only wanted 5kg and requested the manager, the manager came through and she was rude, no name tag and not giving her name. I explained again why I called and she said we will get 25% off the original price and not the price you get when using a smart shopper card, I asked where does it say on the voucher that the discount is for the original price and she said we can go and complain with pnp and not her, I am not sure what kind of customer service this is because its pathetic, Thabong Pnp should just be closed down as the staff is not trained properly. I need someone from Pnp to take accountability of their **** promotions that do not have clear disclaimers.