Voltas — This is mental harassment and the company need to pay for this

I have purchased a window AC 1.5 ton in march 2018 along with the WTA warranty for extra 4yrs. I have purchased this product From Amazon and i have been following all the guidelines told by the company. For the WTA warranty i have received a certificate too from the company. And now after 2 yrs they are telling me that your product is out of warranty and any service comes under warranty like gas filling and repairment won‘t be available for you.
They are denying that we haven’t given you the certificate of WTA warranty and you need to pay for any breakdown and other services.from last 6 days I have been on the Call with VOlats customer care and they are doing nothing. Every time i calls them they asks the same details again and again and nobody has the record for these calls. They mentioned only those information which they want to.
And the guys who were on the call they were telling me that i should have checked before purchasing the product and i need to pay the money now else my AC won’t be serviced or work.
This is mental harassment and the company need to pay for this. From last 5 days, i have called you guys 100 times. And the service center guy also misbehaving with me over the phone that he won’t send technicians to my home.