Prices are changed randomly after customers seen it

I went to Checkers at Mall @ carnival to get a few things for my son going to boarding school, I saw that the Kelloggs noodles were cheaper and I took a picture of the price and when I got to the till the price was higher by R. 4 and when the lady at the till wanted to verify, the price had changed at the shelves. The manager refused to give me the noodles with the price I saw a few minutes ago, I'm very disgusted as this wasn't my fault. The price was changed after I saw it.