Game overcharging by charging the normal price

I stay in Pretoria East a few km from Game Woodlands Boulevard. On Saturday i went into the store and bought somethings which were on special and when at the till the full price was charged. I spent about 20 minutes paying because everything on special was ringing the original price and between the supervisor having to check these things and her authorising the special wasted so much time. Saturday probably marks the 5th time that i have experienced this at Game Woodlands Boulevard and i always complain and say but i noticed what about the X number of customers that walked of the shop without noticing this so meaning you overcharged them? They never give me an answer and because i know this i am always extra vigilant at Game Woodlands Boulevard but this wastes so much time and i think it is inexcusable.