Pays for items they add to your slip secretly

Just went to SPAR ZAMBEZI EXPRESS (cnr Mirca & Marija), and the cashier (Mpho) scanned 3 items that I did not take total R52 and made me pay for it, when I asked my slip she immediately said oops "made" 3 mistakes. (I did get my money back, but if I did not check she would have gotten away with it. I do have proof. So please check your slip ALWAYS.