United Colors Of Benetton — unfair billing at benetton store at dlf promenade, vasant kunj

I got a t shirt exchanged at this store.in place of that, i bought three items. When the t shirt was exchanged, the billing guy subtracted the mrp of the t shirt with the highest priced item i had (Offering no discount, while the store was on sale) asking me to pay the difference. While i understand that the mrp of the exchanged would be subtracted from the mrp of the new item, he deliberately picked the highest priced item, thus making it a non sale item. If he would have exchanged the t shirt with the other products i bought (Which were all higher priced than the t shirt), i would have paid less differential and got 40% discount on more expensive items. I pointed this to the guy post billing because that is only when i realized that i was not given the sale benefit of the item i got the t shirt exchanged with, but he refused to re-do the billing. I lost some money but more than that lost trust on the fairness of the store.