Discount Promotional Prices Not Credited

This is a second time experience such service at Pick n Pay Family The Galleria,the first incident happened a month ago where when I reached the till point,all my goods were scanned and paid via a debit card and I received an sms notification that the payment for goods has been deducted from my account,but only to be told by the cashier that the payment isn't reflecting on her side and so they can't give me the goods,after I posed questions we reached consecus but when I got home also noticed on the discount promotion goods I was charged normal prices which I queried the next day and was told this was caused by technical glitches that occurred the previous day. Yesterday I purchased items in the same store and with my bank debit card and there weren't any glitches but I've noticed that a particular item that was on promotion was discounted for on tillslip. Incidents like these raise many questions.