Extra prices at Point of sale

I went to buy Champaign and chocolates in Mall of Africa. I took champagn which was R139 on special. When I got to the chocolate section I found chocolates that were priced R57 a box and I excitedly took and went to the tills. When I got there the cashier scanned and the chocolates were R99. I explained to her that the price on the shelf is R57 and she stood up and went with me to the chocolate section. I showed her and she showed me other chocolates which were smaller and R54 in price and said I can see that it doesn't make sense for the bigger ones to be R3 extra. I then walked out and left her because she was insisting what I am seeing doesn't make sense