Vat added again after discount

Location/place: Ludhiana

Name of company/service: Calvin Klein Jeans

I went to the Calvin Klein Jeans, Silver Arc Mall, Ludhiana and a product had a 20% discount. During billing, they did 20% off on the MRP(includes VAT) and then added VAT(of 6%) all over again. So the total discount in-fact, was not 20%. In this way they are misleading consumers by showing a higher rate of discount while in-fact providing a lower rate of discount.