**** over Holiday period

I bought a toy for my son marked R479, when I got home saw I was charged R100 extra. I returned to the store with my slip to show them. Their response was that I was charged R579 because I did not have a rewards card. No where on the marked price did it say I would be charged a different higher price. The store manager refused to refund me the difference. How many people are being ****med by this over the festive period, their stores also don't have a monitor facing customers so we can see the amounts being rung up.