Blue Dart Express — Payment done but product not delivered

Address:

BLUE DART EXPRESS LTD SHALIMAR CO-OP HSG SOC, NEAR EMBASSY MARKET, OFF ASHRAM ROAD, AHMEDABAD, GUJARAT, 380008

I've bought a mobile cover from Zapvi.in and the delivery agency is Blue Dart.
The product had to be delivered on 26th December, 2023.
But till now it hasn't been delivered.
I've contacted too many times but every time I contacted to seller & delivery agent, they said that, my product will be delivered immediately.