Paytm — About refund of a product

I had bought a wd my passport ultra 2 tb titanium, but the product sent to me was of differenet model no.i had applied a promocode of 20% cashback which I got after the delivery.when I complained about receiving wrong model no. they said they don't have any replacement policy and I will be refunded only for that, which of course was done.but I had told them that I wanted the product at the same cost and they will have to do something for that and they said that I will be compensated for their mistake, but now they are refusing for the same despite of their mistake. order id-[protected]