How to prove that I am the land owner ?

Hi sir, my dad had purchased a (land) site/ plot of 7.5 cents (area) 15 years back and was Registered on his name. We have all link documents with us. Two years back in 2017 it was transferred to me as gift deed and registered on my name. Now few days back I received a show cause notice from court mentioning to attend a hearing. Some person has filed a case on his relatives in 2016 related to a land and it's hearing is on this month 16th for which i have got notice to attend mentioning that my site comes under their land and it belongs to them. Along with me many other people who's sites are beside mine has received similar notices mentioning same. How to prove that I am the owner? I have all documents, link documents and it's registered under my name. My dad has invested his hard earned money on that and it's completely ours from 15 years onwards. My dad has passed away recently due to brain tumour. This site is his memory to me. How to protect my site from these people? Please help me out. Thank you.