Incorrect price tag

i have been to Woolworths Thavhani mall and every time I buy Item am being told that the price on the tag are incorrect as the vat has increase. why cant you guys put the correct price as I buy something known the price on the price tag is correct and I have been told they will look in to it and every time I buy is the same thing. Woolworth Thavhani is taking advantage of us.