Charges xtra vat during discount period

I made some purchase from woodland karol bagh. There was flat 50% off on most items however they kept announcing that vat will be added. Upon reciveing
The bill it was quite clear that vat was added to the mrp. The amount was 12.5% on footwear. I have found out that it is illegal to charge vat on the mrp as mrp includes all the taxesand they can only deduct the discount and are overcharging in the bargai. I would like to complain again this brand so that they do not cheat their customer.