False advertising

Yesterday I visited checkers Westgate mall to do my Christmas shopping. I was in possession of my xtra savings card thinking that I'll be saving some money as being advertised on television and how was I. First I found several shelves empty for items being on sale and this was at 10am in the morning. The store was not even full so I asked one of the store staff the reason why these shelves were empty and if there was any stock available in order to stock the shelves and was given any reasonable explanation with regards to this. As we were busy with our shopping, my wife was busy calculation the money we will be spending to see if we would be saving any money. As we've reached the pay point, our calculation of all the items we were going to pay for came to R3 950-00 as we rounding the prices. To our surprise, when everything was added up at the till, our total came R3 965-52 and I was asking the cashier how this is possible as we calculated R15 less than her total but most importantly where is the instant savings being promised during advertising. To my surprise, the cashier shows me my slip and said that I've saved a total of R26. I said that it can't be possible because our shopping was more than what we've calculated as we were doing our shopping. I believe that checkers is falsely advertising this instant savings. I could've rather gone to pick and pay and earn shopper points which I can convert to cash when I need it.