What should I do,builder hasn't completed the construction work?

My father has purchased a 1 BHK flat. The builder has completed our flat and handed over to us.But, colony is still under construction and the work is stopped since few months.The builder has completed the individual flats and duplexes from inside and then handed over to the owners. The builder has promised to hand over the property to their owners within a period of 18 months from the date of booking with all modern facilities as promised by the builder.But now, it has been 4 years or more and the colony is still under construction.The flats aren't provided with lifts as promised by the builder.The generator for electricity is still not installed, no community hall constructed,no park or ground constructed yet. No society formed and handed over to the residents of the colony.And many more problems are present.All the residents of the society don't want to file a complaint against the builder, but do want my colony to be complete, well constructed, beautiful to look at and peaceful & modern to live in.Please guide me with this matter and be always grateful for this help.Thank you.