Regarding grade decrease without information

Hi
Every one
I am working with an Pvt Ltd since two years back when I joined I was at grade m10 but now management
Decreased my grade in m11 without
Prior information so I want to know about is it possible or any rule that they can do decrease the grade any point of time when I asked to HR she
Replied that they have revised grading policy
From India, Delhi

1. Please state your current roles and responsibilities
2. How many employee headcount is in your PVT LTD Company?
3. Is your organization where Owner himself/herself sit and do operations?
From India, Pune