Senior citizen parents being forced to leave flat by society president

 We own a flat and live in an apartment with my parents who are senior citizens and we pay the maintenance fee regularly. My Apartment President is a rude person who always disturbs my Parents, he even turns off the lift when guests arrive to my house. He is acting as if he is the owner of entire society. Nowadays he is motivating other people of the society to talk against us. We had a fight previously regarding the calculation of maintenance fees, where he insisted to provide the calculations and asked us to leave the society (It is our own flat and we have the rights not to leave it). My Neighbor next door also had an issue with this president, and an case is already registered against him through nearby police station. But he still continues to disturb. He also writes rude statements related to us in Society Whatsapp Group. Please suggest what action can be taken against such kind of person?