Wrongful exchange policies.

I made a purchase last week during their promotion on ladies wear for the 3 for 2 and accidentally bought the wrong pants and only realized when I trued to fit it on over the weekend. When I went back today to their Somerset mall branch to exchange it for a normal length I was told by the cashier and the PPC on duty that because there is a price difference I lose the discount and that for me was very disappointing. I've spent thousands in that Somerset mall branch. I would not recommend my family or friends to shop there.