Tenant for 35 years not vacating the house what legal action to take

My Father has 1 room in jogeshwari Meghwadi chawl.Which was bought by my granny 35 years back.My granny purchased it on basis of photo pass,She had kept 1 tenant that time who was paying rent of Rs:25.Later on chawl went for proper cement houses build up.The tenant from that day started claiming property to be his with different room no and he stated that our house he had vacant that time & the house which he is staying is his .Two times case went in to our favour but unfortunately judge changed & something happen,My granny passed away 10 years back .but she handed power of attorney in name of