Amazon.in - Package delivered with one item against ordered two

I recently ordered two number of "ECOTARP ***% Pure Virgin Heat Sealed UV Stabilised *** GSM KHAKEE (** FT X **FT) Water Proof Plastic Tarpaulin Sheet" (seller: Deepak canvas company ) from Amazon.in and the package was delivered on *.**.****. On opening the package, I discovered that the package had only one sheet against the ordered two. The delivered sheet was of good quality and I assumed that there has been a miss on the part of the company while packaging and sending. So I registered a complaint with Amazon.in regarding the order and I was informed that there will be an investigation regarding the same and Amazon.in will revert back. Amazon reverted back in a robotic fashion stating that investigation is complete and they cannot issue a refund/replacement.
I have been communicating to the seller and amazon.in multiple times in the past month and the seller (M/s Deepak canvas company) has accepted that indeed only one product has been delivered and Amazon.in has clarified to seller that the customer (me) has been issued a refund as the undelivered item was missed at Amazon warehouse.
On the other hand Amazon.in personnel have replied that they understand that product has not been delivered but cannot issue a refund their ‘investigation’ is complete and absolute. When I asked about the nature of the investigation and how the conclusion was deduced the agent said that it is confidential and cannot be shared. I asked if I can talk to supervisor regarding this which she denied. It is clear from the email that there has been nothing like an investigation is done and just the delivery receipt has been checked. I accept that the package has been delivered to the concerned address. My complaint is the package had one product instead of two ordered and paid. Each of these sheets costs Rs. **** and is not a meagre amount. Clearly, the Amazon.in is in a denial mode and has botched up a fancy investigation to harass the customer. To add salt on the wound, the customer care is not providing any email id for escalation stating that this is final. How come an investigation get over without hearing the customer? The worst part is the customer care doesn't hear what you say, instead, rant a continuous stream of apologies and harp the same robotic tune.
A basic common sense is sufficient to understand that only one product was delivered. Each of the sheet weights nearly * kg. The package delivered was weighing *.* kg (clearly mentioned on the courier note). So it is very clear that only one product was delivered.
Order # ***-*******-*******
Product: *** GSM KHAKEE (** FT X **FT)