Advertised discount not honoured

On 20 October 2015 , I bought 5 books at CUM Books in Northgate. Three of the books were on discount. The discounted price was displayed on a big bright yellow sticker on the front cover. I am disappointed because I was billed the wrong amount on two of the discounted items. The cashier who helped me made small talk about the big discount on one of the books, saying how great the discount was but that the stickers must be removed because discount is over. Fortunately for me he said, I will still receive my discount. On exiting the shop I decided to check my till slip because the total price seemed high. I discovered that I was not given the discount on the other two books (although displayed on the front cover on a BIG BRIGHT YELLOW sticker) I went back into the store to complain and was given a refund of R120. This is not what you would expect of a Chrisitian store!