overcharging the customer and refusing to refund

My friend and I went to KFC for lunch and she wanted the Doritos crunch burger. I asked Mzolisi, which I'm assuming is the manager, if the doritos crunch burger comes as a meal and he said yes. So, we order the food and when we sat down, we noticed that they charged us extra for the chips. When I went back to the tillpoint, I told them that they overcharged us and their response was, with quite an attitude, \you wanted chips with it so we gave you chips. The small chips cost R11