Amazon India — didn't get the product but showing delivered

I didn't get a product but it is showing delivered in my account. There should have given two items in a box but only a single product i got. After complaining about the issue they refuse to refund me back.
They have given the same tracking id to two product and delivered in the same box. I only got the sinlge item. After complaining about this issue with amazon they didn't give me any prove about their investigation and also said that from their side the item gets delivered now they can't do further inquiry. I didn't even sign anywhere or given otp to them how can they marked an undelivered item to deliver.