Tata Cliq - Cash back not received

I purchased Oppo f* from tatacliq on **rd Nov( order no. *********).
It's cost was ***** Rs with **% cash back on HDFC credit card, which suppose to be credit within * months after completion of scheme that is up to **feb, ****.
As I started follow up for not getting cash back from ** Feb through mail, they started giving me dates that wait up to that(three time they gave me date). Then after so much follow up they said on ** that they had registered my complain. Then after that day I received a call from tatacliq asking me my card first six digit and told me that your card was eligible and asked me to send last * month's credit card statement to check.
Then after sending those, after * days I received a mail that there financial team said that your card was not eligible and I will not receive the casback. Then I asked for explanation, they didt reply yet.
Even few days later from my purchase of Oppo my brother in law purchase through tatacliq a mobile from my same hdfc credit card, that time cash back was revived.
It's looks totally cheating