Dispute over grandfather's ancestral property

Lived in up.we have ancestral land and my grand father has three son.in 2003 by mutually grand father diveded property in three but a plot with construction over it located in city divided in two as plot is not as big as it can not diveded in three .they promise that they gave money acording to market rate and they occupied it and pay 1 lack and promise that other pay in some months but after my grand father death they denied any further money and told we already paid all amount . we approaches to realtives but nothing happens .they are dabang type and when we asked about money they simply refuse every time and say we already paid .every thing was did by mutual trust and they don't have any paper or will of that plot neither we have .how can we proceed in this.