Bajaj Auto — Cheat at servicing centre

Dear sir,
I purchased my lovely bike avenger cruise 220 having chassis no. Md2a22ey9jck04685 from vadodra gujarat and had servicing as per servicing schedule while moving to munger bihar there was a technical fault in my bike not starting i moved to nearest serving center and the diagnosed the fault and said that one item magnato is unserviceable and amazed to know that the bajaj motors was changing the same part of all particular lot of avenger bike but the agency did not inform me and changed the item in paper without issuing job card and again it was shocking to know that they have changed wrong grade of oil and due to that my warranty void.
I want to know that how a consumer can know the grade of oil and how to avoid such cheat.
On what basis bajaj motors is giving authorization to such careless agency.
Plz look into the matter and inform me regarding remidial action at the earliest.

Yours faithfully
Dr. Shyam kumar
Assistant professor
Brm college, munger
[protected]
[protected]@gmail.com