Pick n Pay - I was over charged

I went to pick n pay in Bedworth park to buy few items.I got to the till give the cashier my smart shopper card to swipe , cause all the items is less with smart shopper. I ask her did she swipe my smart shopper card to confirm.She replay yes, pay for my items and left the shop. When I got home I look at my till slip, just to realize that she did not swipe my card and I pay normal price for all my items.I pay a lot more than what I was suppose to pay.