Probably you did not take possession and/or raise boundaries and kept guard to keep the possession.
Hope you have the mutation records with all link docs, sale deed etc etc
Lodge police complaint under proper acknowledgment and take help to stop the construction and to make the encroacher leave the site and also obtain injunction from court ASAP.
You may take help for any matter from, elders of your family, competent and experienced well wishers, seasoned PIP’s, helpgroups, community leaders, NGO’s, experienced colleagues, associations, religious scholars/leaders, influential persons, Employee’s/Trade union leaders, help groups for spouses (Husband/wife) etc and find a very able LOCAL counsel specializing in concerned filed of law e.g; Criminal/Civil matters as in your case, and well versed with LOCAL applicable rules, precedence, latest judgments etc …. and worth his/her salt, can advise you after examining all case related docs, inputs, evidences on record.
Obtain proper legal opinion in writing!
Avoid acting on your own on hearsay.
One should not fall for IT’s and entities loitering at online portals to allure unsuspecting querists. There are many threads on such instances at LCI also.
Online discussions are not substitute to in person discussions with a very able counsel of unshakable repute and integrity specializing in concerned field of law.
There are such very able counsels at each location.
Check for such counsels at LOCAL; Civil Courts, HC, SC,..
You can also try for FREE legal Aid from Legal aid center (DLSA) that is usually within LOCAL courts complex..preferably from a very able counsel specializing in Criminal/Civil matters.
Your counsels can advise after examining all docs/record/inputs pertaining to your matter and help you. You can also search threads on similar query in SEARCH option ON left Hand side of threads in Forum/Experts section. Having learnt a lesson, remember to consult beforehand for your matters or any matter about which you are not properly informed.
The FEE of all LOCAL counsels at all LOCATIONS is not high/unreasonable as mis-believed by many.
Many counsels even at State Capital/Metro towns do not demand unreasonable high FEE.
IT is rather at online portals that unsuspecting querists are mislead as per many publications, by IT’s and Entities that pose as some Lawyer (actually LIAR) and flaunt/advertise firms that are not Law Firms (Actually LIAR’s Firms) to believe that LOCAL counsels are not knowledgeable..are incompetent.
In Reality the LOCAL counsels win cases in LOCAL courts at all LOCATIONS.
You can go thru/search the cases contested by any Lawyer at court website.
If the matter involves loopholes concerning DRT etc approach a counsel specializing in such matters as well.