Amazon India — cashback not given

Hi i am a resident of rohtak, haryana. I bought a mobile that is samsung galaxy j7 from amazon.in on 14may 2017. I ordered the phone during the citibank credit card offer according to which i will get 15% of the amount after 3 months of the purchase. Now the 3 months are passed and i called amazon and now they say that the offer was not available on that mobile. But when i ordered the mobile it was mentioned there that i will get 15% as cashback. Amazon cheated on me. My contact no. Is [protected]. Email registered with amazon is [protected]@gmail.com