Amazon India - Refund not being issued by Amazon

My concern is in regards to the order number ***-*******-*******.I am a prime and a very old customer of Amazon. The order number ***-*******-******* is associated with a mobile phone. Redmi Note ** PRO. It was ordered on **th Aug. The phone had hardware issues.. A technician was sent to our house by Amazon who diagnosed the issue as a hardware issue and a return pick up was arranged for a refund. On **th Aug'**, at *:**-*:**pm, the amazon courier person reached my home to pick up the package. He opened it, checked all the items, validated if it was the same item and picked it from my house. I was informed that I would get a refund within ** working days. I called Amazon on **th Aug to check for a refund and I was informed that I returned an old used item. I was shell shocked. How's that possible? The amazon courier person validated and picked the phone. Why will he pick an old used phone for a refund? I am being told by the account specialist that I must return the original product. Where shall I return the original product from? I am ready for a police or any kind of investigation. It is very unfortunate that the customer is not being trusted. I have purchased so many items and never cheated Amazon. I spent **K+ hard earned money in EMI and now I am being told that a refund cannot be processed until Amazon receives an item. I humbly request you to look into it and process the refund.