HDFC Bank — Non receipt of Cashback offer

I made a purchase on an Apple watch on the Unicorn website on 18th Nov 2020. I had opted for the brand cash back offer however I have not yet received the said cash back amount. The offer terms at the time did not state that it was only applicable for PARTICULAR type of cards it simply said ALL DEBIT AND CREDIT CARDS. And now I keep getting told the card is not eligible.