Ravi Group Mira Road — Gaurav samruddhi, mira road

I have booked flat in gaurav samruddhi in dec 2010, when plinth was not even ready builder asked for payment, i argued with builder mean while i paid but in next demand letter builder started writting ineterst for late payment even though i waas paying on time, now in 2015, his demand letter showing late payment charges with interst and penality on interst which is unjustified. Once few months back builder representive asked me to pay advance amount to get removal ofinterst and penalities, i paid rs 2.25.000/ in advance, officer of ravi development signed on paper and all penalities remove but next demand letter for slab showed again same amount and penality on interst... But builders accounts section removes interst n signs but every new demand letter shows same penality increasing, builder is not ready to remove all interst and penalties from system.. Builder has delayed the project still no sign of possesion. Pls help