Hello Sir, I booked an independent house in a gated society in Feb 2017 and paid the 20% of sale c

Hello Sir, I booked an independent house in a gated society in Feb 2017 and paid the 20% of sale consideration amount as part of agreement. In agreement, it was mentioned that it will be completed and give possesion in 5 months. Later, got to know that few of the independent house of this gated society is combinely mortgaged by Tata Capital (because builder took some loan and repaying slowly). And my independent house is also in this mortgage list. As of now, I have paid 20% of sale consideration amount only and contacted one bank.But the independent house is only 50% completed as of now. Now, the price of home and land in this area got increased a lot and builder is demanding extra 10 Lakhs on sale consideration amount to build the same house now. Or he is saying to take your money back. But I don't want my money. I want my house in same sale consideration amount as per agreement.help me that what action I can take or how should I proceed to get my house on my name.