Reliance Digital — Cash back not received yet

Address:

Store Address: CDIT Perumbakkam plot no. 1 & 2, Ground, First & second Floor Perumbakkam Main Road, 5th Main Rd, Perumbakkam, Chennai, Tamil Nadu 600100

I purchased an Air condition from Reliance Digital on 22 Feb, 2020. They offered us 2500 cash back with HDFC consumer durable loan using bajaj emi card. It’s 6 months emi duration. I paid loan processing fees of 700. Now 9 months almost done for product purchased.

They made the transaction at their end and assured us to
credit the cash back after completion of 3 months successful transactions.

Even after 6 months when we did not received cash back I raised compliant in HDFC Loan department staff and Relience store supervisor and commercial manager also.

Now they told there is no offer run in purchased month so I am not eligible for cash back.

When I went to buy Air condition at Reliance Digital, they offered me cash back of 2500 cash back using bajaj emi card that is why I made a deal.

Now, they are told no offer on purchased time and proof are destroyed in system so unable to get the offer document.

How I am responsible for it? Why should I bear the loss for their mistake.

Here are bill details:
Product: 1 Ton Blue star split ac.
Price: Rs 31491

Store Address:
CDIT Perumbakkam plot no. 1 & 2, Ground, First & second Floor Perumbakkam Main Road, 5th Main Rd, Perumbakkam, Chennai, Tamil Nadu 600100