Lenovo Mobile — lenovo k6 power

Dear sir, i have submitted my phone lenovo k6 power to lenovo service center few days back at wonder mall alwar.
I have given my phone to them in on condition and they have returned it to me in dead condition where my phone is not even switching on now. If it was known to me earlier that they will damage my phone instead of repairing it i would never have gone there.
Instead they said that "we are not responsible for this. We had examined and put the phone in well condition and the phone was became dead at its own"
Instead of this i think they had to return my phone to me atleast in the condition in which i have given it to them.
I believe that the service center people are responsible for this loss of mine.
So i request you to please take a required action against this case and get my phome repaired by them because the fault is totally theirs. Thank you