Amazon India — Item returned by me, but no refund given. Amazon call centre says return was cancelled

Address:	603103
Website:	www.amazon.in

I ordered famacart tableware coffee mug borosilicate glass pack of 4, 500 ml on 2 oct 2016 for rs. 2, 697
Order no.[protected]
The delivery was completed, however, as the size of the mug was much bigger than expected, i requested for a return. We waited for 2-3 days for the item to be picked up, however, nobody came to pick up the return. Thereafter we made several complains and finally the item was picked up from our home on 15th or 16th oct 2016.
Since, i did not receive the refund till 1 dec 2016, i got in touch with the customer care. They informed me that the return was cancelled. When i said that the return was not cancelled, rather it was duly picked up from home, they asked me to provide a return slip as an evidence. Unfortunately, i do not have the slip. I think the courier person never gave me the acknowledgement slip.in absence of the slip amazon is refusing to process the refund.
I asked them to investigate the matter with the courier agency. However, there is no help forthcoming. I have been cheated.
There seems to be a fraud committed by the courier agency who picked up my item and intentionally did not provide me the acknowledgement slip with an intention of defrauding me. The courier agency instead updated the record as pick up cancelled. I think they are trying to defraud innocent customers who do not know the process of returns. If some one forgets to ask for the pick up acknowledgement, then they swindle the returned item and update the courier record as return cancelled.
I want amazon to kindly investigate the action of their courier partner - ats courier who was responsible for the pick up. This type of fraudulent activity has to be stopped otherwise innocent customers like me will suffer. I want amazon to kindly refund my money which is now due for more than 45 days.