Masroor From Mumbai want legal help in Property / Ancestral Property / Will

I booked my flat 1 and a half year back and it is registered now i came to know that there are S. R. A. building constructing just behind my building they didn’t tell this on the time of booking now i want to cancel my flat but builder persons are refusing to refund my money. Kindly help me out as i paid 12 lakhs as 10% and 6 lakhs for Stamp Duty & Registration. Thank you very much