Flipkart - Received wrong product

On **rd March ****, I had ordered Ambrane Power bank *****mAh, but on **th March ****, received MI Power bank *****mAh (that too a used one) inside an Ambrane Power bank *****mAh package. I immediately filed for a replacement giving reason as received a damaged product as there was no option for received wrong product. Flipkart was taking too much to solve my issue so I decided to talk to a customer executive on **th March, ****. The person on the other side of the phone told me that he is filing for a return as received a different product or else my replacement would be rejected. The expected pickup date was *nd April, ****. On *nd April, the pickup agent called me and asked me the reason for my return. I explained him the whole situation. He told me that he will talk to the manager and call me back with a response. I did not get a call back but at *:**pm I received a message saying that my return was cancelled because I decided to keep the product. I was shocked to read the message. I immediately called the agent using the number provided to me by Flipkart in earlier message. The agent told me that his manager had told not to pick up the item or else the amount would be deducted from the agent's salary. I told him that I did not authorize the cancellation. He responded That the manager has authorized and he cannot do anything about it. I asked him to connect me to the manager but he regected. I contacted Flipkart customer support through app and through Twitter. I got a call the the person on the other side was themselves confused but they ensured me that my matter would be solved.
Being a loyal customer of Flipkart from past *-* Years and a Flipkart Plus member for more than * months, I feel like I have been cheated by Flipkart and it will be very hard for me to trust any online shopping site in the future. They aren't looking into the matter at all and just wasting my precious time which I could have utilized doing some other more important work.