White House Industries Private Limited - Manufacturer refusing to honour product warrenty

I purchased a geyser from their local distributor couple of years ago. Last year, we had an incident and we were without hit water for a week. It is the same thing again this time. When I called them yesterday they are asking for the original invoice which I could not locate. I did however provide them the product serial number and images etc and dealer information. They are saying I will have to pay for the repairs despite the fact that the product us under manufacturer warranty.