Nykaa.com - Wrong item delivered return denied

I ordered a green dress by the brand ** dresses from nykaa app but I received a pink dress from the same brand. Now the online merchant is denying it saying that they a use several checking measures before delivering a product and asking me to send them photos of the product. Even after sending them so many pictures clearly showing the item I received including the brand tag the price tag shipment number all of them they are denying my complain and not initiating return. They do not even have and exchange policy . Engine fat their return policy is valid for only * days. They are harassing me since **st of January.