Honda 2 Wheelers India — knocking sound in engine

Address:

Tapi, Gujarat, 364660

Augest 2016 i purchase unicorn 150 but in 1 year after knocking soung comes in engine so i went to showroom for solving my problem he told me that piston wear and valves to be changed. I asked him how it is possible in new unicorn so he tell that problem come in unicorn manufactureing defect. He change pistion and valves but only piston on warrenty period so he take money for other parts.
After some days that sound also start in engine. Pls solve this issue. Why knocking sound in new bike. If this issue frequenly happend then what should i do.