Whom should we complain if the builder like "ATS" do not fullfil the promise of handing over a unit where one can live?

Q: Possession Date: Aug’ 2012
 Payments :
1. Full Unit Price was Paid in Advance at the time of Booking,
2. All dues and Full Maintenance for next three years paid prior to possession.
 Possession Condition:
1. Unit was handed over by builder in unfinished condition with a verbal commitment & promise to finish the unfinished work soon including final painting. Till date nothing has been completed i.e. it's not in a liveable condition.
2. Also till date Car Parking has not been allocated, for which
payment was paid in full.
 Interest on delayed Construction:
1. Interest was adjusted in partial (till May’2012) with a promise to make final adjustment in few months, result, no response from the builder on balance interest refund.