Extra charges imposed in last demand as interest delayed payment

Sir, I had purchased a flat. 10% was given as booking. Agreement was made in april 2012. Now loan process was started. Builder was demanded installment in october 2012. Now, the loan was approved by bank in march 2013. Delay is due to uncompleted papers of builder side. As per the demand made by builder at that time, bank paid full amount. In demand letter, no interest on delay payment was mentioned. Even after that in same way payment was made by me or by bank based on demand made by builder. In no demand they declare any interest charges on delay payment. Now in final settlement, they mentioned more than 3 lakh as a interest on delay charges even after the settlement of 95%. If there is any delay from my side or bank side, then they should demand for the delay. But they never demanded in any demand letter on which alll payments paid. Please guide me whether i am liable for interest on delay payment, while up to 95% payment, they never sent me any demand for extra payment for interest on delay payment. Also the project is delayed by more than 1 year. Please guide me, what should i do.