Overcharge

On the 5th Sept. I purchased a bunch on celery from Makro P.E.. ... no price visible. on looking at my till slip a day later, I saw that I had been charged R21.95..... HOW IS THIS POSSIBLE. ... if PNP can charge R12.99 how can Makro justify charging nearly double for this?? When I phoned to query this, their manager says that's the price, to which I respond what I will warn people to not buy there as they will be **********, his response is \OKAY COOL?? "Seriously"