How can a teller read the incorrect barcode on 3 items?

Went to till 17 at Woodmead and finished at 15h47 at the till. II had chosen 3 items that were reduced. I noticed that that the last item did not reflect the discounted amount and had that changed. On examining the bill I noticed that 2 other items reflected the higher amount and then obtained a refund. I asked for the manager who had apparently left. One of the staff walked to the offices to ask the 2 in charge to come to the shop floor even though there was a phone there. nothing happened. I asked for another staff member to phone the offices. I spoke to the Admin Manager who eventually came down. The manager stated that the normal barcode had been read. I asked why the teller had not simply put her finger over the normal barcode. No answer. From exiting the till until I left the store it took over 30 minutes. I informed the staff that my next purchase would be at Makro