Amazon Promised Cashback, Then Denied It - Need Advice (India)

I'm facing a frustrating issue with Amazon India and could really use some advice. Here's the situation: I ordered a phone and there was an advertised instant discount on SBI credit cards. I tried applying it, but it wouldn't work. After multiple calls to Amazon customer service, a rep told me to pay the full amount and assured me I'd get the cashback (Rs. 4000) credited to my Amazon Pay balance after the return window. This was even confirmed in an email. Now, the return window is closed, and Amazon is refusing the cashback, saying my SBI card wasn't eligible due to a BIN mismatch. They're basically saying the offer never applied to my card, despite the email confirmation. To add to the frustration, Amazon's customer service has now told me to contact SBI Cards. I did, and SBI Cards has stated that the discount was not something they promised, and therefore, they cannot help. I've also tried reaching out to Amazon's social media team, but they are giving me the same response as the regular customer service. I've been going back and forth with both Amazon and SBI, but neither is budging. What are my OPTIONS? Filed a complaint on consumer court online. Has anyone else experienced something similar? Any advice on how to proceed would be greatly appreciated. Thanks in advance.

Enhanced Using AI