Builder delayed possession, asking for interest on delayed paymen

I booked flat in July 2013 with one of the reputed builder in mumbai. It was construction linked payment. Due to some issues, I had agreed with builder on alternate financing option - Parallel funding with banks where I did registration on 9% of payment and rest will be disbursed by bank after agreement.Builder agreed for that and waived off all interest at the time of registration. However the same was not reflected in demand letters. I informed them in writing but they said it will be corrected. That did not happen till date. I have informed them on regular basis. Now in April 2015, they are asking for interest of around 5L from 31st day of booking, which was not corrected that time. I was about to cancel the booking at that time but they said you can go with this without any issue. Also the possession date as per agreement was Dec,2014. But they have issue the letter for taking possession in April,2015. I have paid all dues and met in person for weaving off interest. In meeting, they said OK, but now again asking for same amount. 1. The interest on delayed payment is wrong amount, which they had agreed earlier. 2. They had only one banker, which had delayed in loan disbursement. I had shown interest in going for other banker, but the builder did not allow saying you have this option only 3. I have been suffering huge financial losses and mental suffering due to delay in possession and demand for huge interest component 4. They have delayed possession by 4 months. Also they have changed some of the internal amenities like Grills, now they have provided inside grills rather than outside of the apartment So wanted to know how do I handle this situation, is there any solution I will get in consumer court I have no money to pay huge and incorrect interest component of 5L