Check your tillslip! Pick 'n Pay *******'s

I bought some items that were on special at pick 'n pay, I don't usually check my till slip but this day I had, I noticed I was charged incorrectly for 3 items. I go back to the store, they do a refund, on my way home I look at the slip - the refund wasn't calculated correctly, I had been short paid, I contact their customer care. over a 4month period - still no resolution, and had 3-4 incidents thereafter of being charged higher for sale items. poor customer service when dealing with them directly. shopping was done with a 7month old baby after a work day - I should be able to trust the prices on the shelf not perform an audit of every bill to avoid being **********