Reliance Retail Limited - Purposely committed false cash back offer

I went to buy a particular model of Samsung Refrigerator and found prices were higher what other competitors were offering for the model. I discussed with the senior sales representative of the store who attended me after junior salesman was not in a position to offer the best deal. He assured me the best deal I would get when I said I was getting **% cash back from other sources HDFC Credit card swipe. He assured me that even Reliance will be offering **% cash back if I swipe Hdfc Credit Card. He asked me whether I was buying on emi to which I told him that it was full in cash. He assured me with his mathematics that I will be getting the best deal and price will be similar and better to what other competitors were offering. He brought his calculation to the deal I was getting below *****/- for the product after cash back. I was told that it will be credited after ** days to my Hdfc credit-card account. I have been following since one month for cash back not received. Now they say it was only applicable if I had purchased on EMI which they purposely concealed at the time of the deal. I did question at the time of purchase (not going into much detail trusting their word) about Hdfc offering only *% cash back to which senior sales representative said that over and above *% from Hdfc I will be getting another *% through the store. I asked how I will get the other *% to which he said it would be via Hdfc & reflected in my credit card statement after ** days. Now the store is coming out with excuses that there was no such offer and would compensate me if I buy any new product from them. Sadly nothing in writing has been given so I know I have been cheated as sales team knew I was buying outright and not in emi.