Builder is charging interest on delay in payment.

Dear Sir, I booked one flat in 2006 in jaipur with one builder and later on builder said that project is not not coming and they transferred to another project in august 2010. after that we were asking them about construction work and any payment due on us but they said no payment is due. later on they again transferred it to another tower at same site in july 2013 without asking our views. they just send a letter that your booked flat has been changed from one to another tower. later on they send a demand letter in january 2014 to pay money for casting of all four floor at once. our payment plan was on construction link payment on casting of each floor with minimum time between two payment 60 days, We paid complete amount in march and april 2014. but they never send any demand letter on casting individual floors as per payment plan. they are charging us interest in delay in payment and not accepting and compensation in delay for possession as they send e-mails that possession will be given in October 2014. we are still waiting for possession.