Unimart Carnival Poor Customer Service

I went to Unimart Carnival City on Saturday 6 January to get a school bag. We chose a bag, ALL bags on the shelves were marked at R 500, the bags were not individually marked. When we got to the till the bag rang as R 700, i brought it to their attention that this was incorrect. They called the manager, whose attitude was he doesn't care what the Law states, he was not selling me the bag for the price stated on the shelves.