Landlord asking to vacate room in name of deceased grandfather

There are 2 rooms (not a flat but individual rooms) in the building where we used to stay earlier. These are on rent basis. Now we are staying in a owned flat. No one stays in those 2 rooms. One room in name of my father and other in name of my grandfather. Rent was being paid separately for both the 2 rooms and two separate rent receipts were being issued by the landlord, in name of my father and grandfather respectively. My grandfather died in 2009. We dint get the name transferred for the room which was in his name. We continued paying rent and rent receipts were issued as earlier. In 2012 (Feb) the building was sold. The new landlord started trying ways and means to get the rooms vacated from many. Upon getting to know that one of our rooms was in grandfathers name who had already died, he asked us to vacate the room.My father gave a letter to the new landlord asking him to transfer the name from my grandfather to him. My father has 3 brothers and this letter was duly signed by all three of them stating no objection. The new landlord did not even accepted the rent and we tried sending it through money order which he refused to accept and hence returned it. Than onwards we started depositing rent through rent control route. Now in May 2014 (i.e 5 years post death of my grandfather, and 2 years post his taking the ownership of the building), the landlord sent a letter through its lawyer, asking to vacate the room which is name of my grandfather. Please advice what can be done here. Just to inform that no one stays in either of the 2 rooms - we have electricity connection in both the rooms and get 1 single electricity bill in name of my father - we keep on visiting both the rooms for necessary cleaning activities etc - there are almirahs, beds etc lying in the rooms..