TRANSFER THE OWNER SHIP on death person

Dear Sir, We have two flats with one agreement. After death of my father we have submitted the documents to builder's office to change the name of my mother as owner of flats. My one brother has not signed on documents as NOC but other has given NOC.Builders had changed the name. Property Tax and Maintenance bill starts s coming on my mother's name. After four year society has found and now society has registered the name of death person of my father. Maintence slip is giving on my mother name and property tax is coming on my mother name.How can society registered on father's name who is the death person?