Amazon India — I was mis-informed about the cashback that I was eligible for and now it can't be returned

I bought two products Samsung Galaxy M21 (Midnight Blue, 6GB RAM, 128GB Storage) and Dell G3 3500 Gaming Laptop 15.6-inch FHD 120 Hz (10th Gen Core i7-10750H/8GB/512GB SSD/Windows 10 Home Plus & MS Office/NVIDIA1650 Ti Graphics/Eclipse Black) D560260WIN9BE from Amazon and I was under the impression that I will be eligible for a cashback of INR 9000 (INR 3000 instant cashback + INR 6000 Amazon Pay balance).
But on not receiving this cashback for 5 days, I contacted Amazon and I was told that I needed to wait for a few days(6th November precisely) and I will definitely get the cashback(attached recording for the same).
Then when I didn't get the cashback on 6th November too, I called them again on 8th November midnight and I was told that the product that I bought was not eligible for the cashback.
Now the only reason that I bought the phone was because of the cashback and if there is no cashback then I would like to return the prouct but the problem now is that I am being told that the return window got over on around 6th November(very conveniently so).
I don't want the product without cashback but I am not being given any option and I am being made to stay on call with the customer care for hours before they disconnect my call. Please help.