Property related issue

5 years ago

Dear Team

We are residing in Faridabad and my mother has a plot in the district Rohtak of Haryana state. This plot was purchased by my mother 5 years back (in 2013). My Mother also constructed boundary wall and placed a gate with lock and also placed a Name plate on the Gate. My mother also have registered deed in her name for this plot. We visit this plot occasionally.
One person (say Mr. X) with the intention of grab this plot broken the lock and placed his own lock. He also removed name plate of my mother.
On inquiring this with him, he is threatening to kill if we go at the plot and is saying that now he is owner of this plot and he has also arranged registry for the same also(though he has not shown).
We have given application to police post for the same though Mr. X has not appeared before police for investigation.
Please tell me which type of offence is it and which section is applicable in this offence?
Whether police department is bound to lodge FIR or not. If police deny to lodge complaint (FIR) what options we have?
Which section are applicable in this offence which should be there in FIR if police lodges FIR?
What precaution we should take so that case is not unnecessary be weakened by the Police Department?
Important Notes
1. This is a plot not a house.

2. My Mother has purchased this plot 5 year back from wife of Mr. X after paying full consideration.

3. Wife of Mr. X is also involve in this offence.

4. They have never challenged registered sales deed in my mother Name.