Royal Enfield — engine fault recognised at reading of 1500 k. m, and the engine re-assembled at reading of 5034 k. m without obtaining my acceptance.

I had purchased a royal enfield-classic 350 gun metal grey bs iv from the dealer amar auto’s 603 kanti nagar main road, swami dayanand marg, delhi 110051as on 05 july 2018.
I am very regret to write that during iind free services, i complained with showroom service engineer that bike in 2nd gear feeling uncomfortable while driving. But every time at showroom they are simply doing oil check service and returning vehicle without addressing my complaint.
During ivth free service the company re-assembled the engine without obtaining my acceptance. We used this bike at plane road and there is no any accident occurred, then why fault occurred in the engine. It seems that fault is carried out from manufactured stage. We paid you for high quality and strong engine and not for a faulty engine. The quality of engine goes down after re-assembling. The engine still have some fault.
Thus i am requesting you, please changed its faulty engine as early as possible. I hope, you will provide good quality of product as per terms of contract, otherwise i know my legal right.