Hero Motocorp — black smoke coming and engine sounds

Address:

Visakhapatnam, Andhra Pradesh, 530026

I have purchased a hero karizma zmr 2014 model in feb-2015 from sri shiva shankar hero showroom visakhapatnam. My bike has some very critical problem with the engine, and it is a manufacturing defect. I am facing it from the beginning when i bought the bike. And i have visited about 18 times to the service centre regarding the problem, but i have not received much of a response from the service centre. Present engine noise sounds and black smoke came out. Service person checked and engine was boar problem. Need to change the boar. I have bought this bike 4 years completed feb-2019. I have an 5years engine warranty, please provide information what can i do