delay in possession and adamancy shown

Location/place: new delhi

Name of company/service: piyush buildwell india pvt limited

i booked a flat 4 years before with possession due in sep 10 as per agreement but now company not replying to my letters and director /MD not speaking on phone for needful.only customer care sometimes talk but do not transfer call to higher ups.
what a game.we have remitted our hard earned money to them and they are not listening us. as per agreement they are to start [panelty clause but they are not doing anything.
will someone help and guide.