property fraud

(30/5/2011)we gave him a loan without interest of Rs. 2crore50lakhs(30/5/2011)..we booked a flat(4/7/2011) by giving 11000 rs cash on 4/7/11 . on 21/7/11 the builder returnerd the 2 core 50 lakhs and on the same day we signed the agreement on a 100 rs stamp by giving him an account pay cheque of 2 crore 50 lakhs. In that agreement builder mentioned the he has aquired building permission from a municipal corporation.we booked the flat to save property gain tax.we booked the flats but the builder didnt give flat though he said that he would give our respective flas within 15 months.the land on which our flats were booked wasnt on the builder's name. By RTI act we found the the munnicipal corporation hadnt given him the permission to build the flat till date it has been 3 years he hasn't given us our booked flat.we sent a criminal legal notice to the builder to return our money with interest and he said by sending a notice that "I gave you the flat just to save u from property gain tax so there is no point in giving u all those booked flats and the booking was builder's money" so what shall we do to get back our money with interest?