Amazon India — redmi 4 black

We ordered redmi 4 (Black) 64 gb amount
9499 phone which was delivered on october 21, 2017
Order number[protected]
Order date - october 16, 2017
It was offered 10% cashback which was to be in our account by jan but months has passed, there is no 10% cash in the account.
Please response as soon as possible, we called customer service but even they haven't responded.
Thank you