htc mobile service provider, Raipur is not giving the phone since last two months

i have given my mobile htc desire816 to service center of htc, Raipur on 20/08/14 stating my mobile phone touch is not working when i contacted them they said mobile phone mother board is broken by them so we demand to replacment of mobile phone from that day they are not giving me response they always says we will contact u in 24 hours, it is now two months please take necessary action against service center of htc raipur
mobile imei no.-352795061928254
S/N- fa47mz01520
service center job no.-RPR004-0001286
my contact no. is 08817709143