Bajaj Electricals — Complaint about want of bill

I have purchased calentawater heater in the year 2015 from saravanvastores chennai. The warranty period is 7 years. The purchased computbill was erased after some months. Now iam having warranty card with me.
Now the geyser is not working. I have registered the complaint in the
Customer care centre.
After inspecting the geyser the technician reporting that the company needs the bill..The bill what they are giving it will not stand for long time.
I request your self to looking to the matter and do needful.