HDFC Bank — Cashback offer

Address:

Chennai

In the month of Oct 2021 i have purchase an Iphone 13, at that time there was a launch offer with cashback of 7000 rs which will be credit upon completion of 120 days. regarding this i have called customer 3 times in which 2 times they have said that it will be credit on upcoming month. i got upset and on 3rd time i have asked them to raise complaint and all of the sudden they are asking me for proof. With what proof they have said that it will be credited in upcoming month. and after asking this question they are asking me to check with Merchant. In this case Merchant is so clear offer is provided by bank and it is no way related to us. HDFC is making advertisement of cashback making people to buy the product and they cheat on this kind of Cashback offer.
My point is so clear HDFC doesnt have any data base on cashback. they have all my data in one touch do they need proof.