unfair trade practice and cheating

Madam/ Sir, We are a group of people who have booked for housing units with a builder in Greater Noida, UP. We have all paid 100 % and the possession is delayed by 18 months now. We have been charged interest @ 18 % for being defaulter where the construction linked plan failed since construction was not complete and we could not release payment against the unfair demand raised by builder for construction not completed. Now despite all this the builder refuses to give penalty for delay which is there in the BBA. The builder after collecting the last payment now wants that the home buyers give 2 yeas post dated cheques for maintenance otherwise he will not complete the units. Also the work is not complete and many houses have water seepage during the rains this month with plaster falling off Just do not know what to do as we have to pay rent plus BANK EMI"s for the loan taken and also have problem with school admission as all of us currently reside in Delhi. Please help as to next what to do