Hero Motocorp — sudden high speed of hero duet

I have purchased hero duet from narayani traders, pakur 816107, jharkhand on dated[protected] chasis no mbljfn022hgj07345 and the first servicing was done on date[protected]. When i and my colleague were returning from office on date[protected], suddenly the speed of the hero duet was increased from 20km to 60 km. I tried to decrease the speed but it was continuously increasing nature, due to this we got injured. We have called service centre regarding the incident, but no proper response received from them. Kindly look into the matter and provide us proper service and safety while driving hero duet.
Thanks & regards
R. Bharti