Show Off — Product not been exchanged

We purchased the product ...wanted it to be exchanged. Initially they asked for bill...presented the bill...then they said heavy dresses can't be exchanged...when we said we were never informed about this ...they somehow pin pointed some damage which was probably there at the time of purchase and we didn't notice..so now at the time of return they said it's damaged we can't exchange. Clearly we were cheated and I would like to seek justice for the same.