Builder died case

Hello sir ,sir i booked a flat in 2010 and given 40 %(by cheque) amount of my flat but in 2011 the builder died and his family members transferred the all rights of that land to a another partnership firm then that film transferred all the rights to a next firm .now that firm had made a new building with new name .and he is not responding to us sir please suggest what should I do to recovery my hard earned  money .