First get enough evidence to prove such encroachment. You have to approach to Municipal authorities and apply for surveying of your land. They collect nominal fees and provide you survey report. At the same time, you have to file RTI Application to Municipality/corporation and seek a certified copy of municipal approvals and maps of the encroacher. Approach to a competent advocate with evidence of such a survey report and copy of the municipal plan given and he can certainly guide you in both civil and criminal action.
The advocate who can handle the case will explain you what is a civil case and what is a criminal case and the chances of claiming damages in civil case for mental tension etc.
What is the relevance as to damages when the suit for damages already pending. What is the present stage of the case? Have the defendants filed their written statement?
Moreover, once the matter has reached the civil court, the procedure for ascertaining the extent of encroachment is to get an Advocate Commissioner appointed to investigate and report to the Court.
Sir, you may refer to this Article from para 5 for better understanding of the query
https://www.lawyersclubindia.com/articles/settled-possession-7381.asp