Lenovo — Complain about mobile handset

I have purchased online one lenovo vibe K4 Note mobile handset from amazon of Rs.11999 on dtd 26.04.2016 bearing Invoice no .KA-BLR[protected]. But after three months it was not functioning. I approached Lenovo service center, Patna then he told that mother board is damage . After charging Rs. 2500/= he repaired the handset on dtd 01.09.2016 & gave warranty of one month.But even before one month again my mobile handset was not functioning. Again i approached Lenovo Service Center, Patna on dtd 21.09.2016 but he refused to repair again stating that its mother board is again damaged
My grievance is that how the mother board of my mobile handset defective within 3 months . It must be manufacturing defect.
So, either replace my mobile handset or refund the amount