Overcharged at Pick n Pay

I shopped at Pick n Pay Cornubia yesterday and purchased to the value of R168.72 but was overcharged by R40. After making further purchases at the cellphone kiosk, I went back and queried the overcharge. They refunded me R30 after some time. After collecting my refund I checked again and calculated for myself what I should have payed and found that I was supposed to be refunded R40 because I was initially charged R208.72. So I went back into Pick n Pay and pointed it out to the cashier. They eventually refunded me an additional R10. Time wasted and it made me late because I had to be at a family meet at that time. No refund transaction slip was given for the R10 though. Everybody please check your till slips to see if you not being overcharged.