HDFC Bank — Cashback Not received

Hello this is Sanket Kumar from Hyderabad holding a credit card with HDFC bank.
I have purchased an iPhone on Nov 02nd 2021 and was entitled for a cashback offer of 6000.
Until today I have not received the cashback and having going around circles with the HDFC customer care team.
I have reached to a stage where I had to escalate to the HDFC priority redressal team with a hope that they would help me.
But Answer is NO.
They're rude enough to reply that I am not entitled for cashback when my bill clearly says that cashback applicable on my transaction.

I would like a resolution to this as to when will I get the cashback of 6000.