Pricing of foods

I was just at the shop where I tried to buy food, pork and pap. The pork was measured at R 12.24. When I wanted to pay for it, the cashier refused to scan it. I was then told by the cashier and manager that it was wrongly marked. I informed the manager that the price stipulates the offer made to me that I accepted. The pork was marked again and came to R 25. I refused to pay the second price as it was not the offer made to me. The staff and manager is badly trained and this do reflect badly on this shop. Up to date I was a regular customer.