Amazon.in - Item picked up but didn t get refund

I have bought many product on **th May, **** and out of which one product that is, Sandpuppy Heating pad was defective which delivered on *nd June and due to defective battery I have raised a replacement for it and after that on *th June they picked up the product and then I have waited for the new item till *th June to get delivered and then I have cancelled it as it was taking longer time.
But after cancelling I am expecting a refund which I have never received. Also, I have called and chatted with Amazon customer care more than **th Times from *th or *th June till today **nd June and every time they said to wait for ** hours to fix it. which they never fixed. According to them, the product never picked up but from our end it has already been picked up by the Amazon Delivery guy.
This is now their responsibility to check where their product is, but I am not getting any response from them so I am writing to you.

Kindly help me with this issue, this is really a headache for me now. the product amount is ****/- but the issue is I don't have the product and also my money has gone, which I want back.