Specials as advertised - not registering at the tills with senior staff knowing this

I shopped at Pick n Pay Faerie Glen on Sunday 22/07/2018. Many specials were advertised all over the shop (buy 5 for R100, by 2 for R40) but when I got to the till, none of the specials were registered and if I did not ask about why the prices were not as advertised, I would have paid full price for the products. After I enquired about the price, the cashier (acting shocked) called the supervisor. The supervisor informed me that they are all aware of the system not being programmed correctly (including the cashier), but if I can tell him what I bought, he would manually over-ride the prices to the correct price - I could only remember half the stuff that I bought, I only saw what I missed when I got home. I was shocked that they were all aware and when I asked why they are still running the specials, the supervisor said it couldn't be stopped. Why on earth would you runs specials, knowing full well that the tills are not registered to calculate the discount? This is shocking and totally in breach of TCF - how can one ever trust a company that knowingly cheat their customers?