HDFC Bank — Didnt received the cash back

I bought iphone 7 worth 31500 from FUTUREWORLD chennai on 18/06/2020.
As per the offer i was supposed to get a cashback of amount 1500 within 120days as i paid the amount using HDFC debit card.

Its been more than the given time period and still haven’t received the cashback. Tried contacting the customer support team but unable to reach because limited number of agents available due to lockdown.
Look into it, this is very frustrating and not a good customer service.

Thanks,
BANU PRAKASH K