Airtel — fastag purchase cashback not received.

I purchased fastag from airtel on 28 november 2019. I was and i am a gold member of the airtel app. It was showing 100rs cashback in my billplan itself at that time for purchasing fastag from airtel. Hence, i purchased it from airtel.
Transaction id for fastag payment is ft[protected].

But i did not receive my cashback. I contacted customer support at [protected]@airtelbank.com. But still the problem was not resolved. Nobody informed properly why the cashback is not credited. It is more than one month now. All i got was case id numbers.
[case:4436621], [case:4446639], [case:4498708]

Even in the month of december and january, 150rs cashback plan is running for gold members on purchasing fastag from airtel.

Hence, i feel so disappointed that i didnt even get the 100rs cashback which was there in my billplan. Even though cashback plans are still running in airtel. Why am i being excluded from that offer. Airtel app still says, free fastag but it did not turn out to be free for me as i did not receive my cashback.

I have attached the screenshot of my billplan during that time showing cashback offer and fastag purchase transaction history.