Lenovo (INDIA) Private Limited - Not providing cashback

I have purchased Legion *i for Rs **,*** on *th Jan. I made the purchase through telephone support with Pre-Sales team. At the time of purchase, representative told me that i would be entitled for *% cashback (approx Rs ****) if i pay through HDFC. She sent me purchase link on my mail id and told me to make the purchase. I used internet banking for obvious reasons and she told me that cashback would take approx * months where the backend team will validate & process it. Now after * months, i have been continuously following up with them on both mail & phone, they are telling me that i will not be getting cashback since i didnt use debit/credit card while making the purchase. But this was not informed to me by lenovo representative at the time of purchase. They have clearly persuaded me into buying their product by misleading with false information. Now i am in pathetic situation and requesting them over the mail but they are denying that its their fault and saying that they cant help. Please help me as i have only purchased keeping in mind that i would get cashback and they have cheated me saying that i will get cashback and now they are saying that they cannot give cashback. I have call recordings, mail evidences to support my justice.