HDFC Bank — hdfc bank tanishq 5% cashback offer on hdfc card

I purchased jewellery from tanishq through my hdfc debit card on 12th august 2018. As per running offer i was supposed to get 5% cashback if paid through hdfc credit/debit card. 6 months already passed but till date no cashback received nor any communication is there stating the timeline for cashback.

I have already tried to contact the customer care, but everytime the call gets disconnected after sometime. And no complain has been registered.