Check your promotion prices at the cashier

People should always check the prices on their promotion at the cashier. They never seem to update their system with thd promo prices. 2 nd time in 3 days this has now happened to me. It took them around 20min ( of my time) to update the system. That was at 14h24. My question is how many customers got overcharged before this time not seeing the one day only price advertised on social media. I have reported a similar problem to Spar HQ, no feedback.