Please provide more details.
As a customer you should always insist on making a stamped and registered agreement when you purchase immovable property. Only such a stamped and registered document is considered evidence in the court. Why did you make payments upto 50% without such an agreement. Have you got receipts with proper revenue stamps for all the amounts paid and have you paid by cheque?
Even if you go to court, they may not consider the papers that you have as evidence in the absence of a registered agreement. However, you may approach a consumer court with all the papers you have and looking at the circumstances, you are likely to get fair justice.
Also after your case has been resolved by the consumer court, please visit some sites like mouthshut where customers can put their complains against faulty service and products so that other customers are warned and they can learn how to resolve such issues.
Wish you all the best.
S Jadhav