Builder not giving possession and demanding more money

I brought an apartment in 2013 in Guntur, AndhraPradesh. I went with 40% down payment and 60% loan. Paid the 40% during registration in 2013 and remaining amount released from bank depending on the status of the construction. Builder registered the UDS share of land and taken a registered construction agreement from me. Construction is delayed by a year and is completed now. When i asked for the possession, builder charged interest @ 24% saying that i should have paid the entire amount in 2013 though he is handing over in 2016. Construction agreement clearly says that i have to pay 50% on completion of slab,40% on completion of brick work and remaining 10% at handover. Also says that builder can charge 24% interest if there is a delay in payment and builder will pay 3000/- if there is a delay in construction beyond 24 months. Builder is staying in the same block as mine and arranged solar heater, CC camera and few other items for only my block and charging 1 lakh extra (This was never told to me). I am NRI staying in USA. I am calling him from last 6 months, sent my father few times but he is not agreeing and keep adding interest every month. I am NRI and not sure whether i can file a case from here. Can you suggest how should i proceed. Thanks In Advance.