Amazon India — cashback not received against order no.[protected]

Address:

H.No.225/2, Rishi Nagar, Old Patwar Khana Gali, Hisar, Hisar, Haryana, 125001

I have ordered for redmi 7a from amazon on 20.10.2019. The details of the cost of the mobile as per the order is :- subtotal rs.4999-instant cash discount rs.499. Accordingly i have paid rs.4499 in total.
There were two offers, first is rs.499 i. E. Instant cash discount and second is rs.500 on payment through rupay card which was to be credited as amazon pay balance.
I have ordered with rupay card ending with 4719 but the cashback was not received against which i register a complaint in amazon on 22.10.2019 and many other times and always it has been intimated to me that i am eligible for the offer and the amount will be credited to my amazon pay balance in 2-3 days, but after several requests my cashback has not been credited.
Today i. E. 27.12.2019 i contacted with amazon and it has been intimated to me that i am not eligible for the cashback.
While my friend sonu ordered for the same product on 23.10.2019 and he get the cashback of rs.500 on 24.10.2019.
I said i ordered with rupay card as per the offer condition and asked for the reason why i am not eligible and it has been intimated to me that the detail of the same is not available with them.
Please help.