Zudio - Return value not same as purchase value

I bought a dress offline for *** rupees, the dress is of a smaller size, when i went to exchange the dress, they had no piece of the next size, so i decided to return the dress, but they say that i will get a credit note of only *** as there's a sale in which the value of that dress is only rs ***. I wanted to return the dress as is of no use to me.