Property Sale Fraud what to do

I had sold my house in year June-2016 and Actual value agreed with buyer was 36lacs but on the day of execution of agreement buyer approached with request to make agreement with value 31.5 lacs, because buyer could not arrange full agreed amount on the day of execution of agreement. Since buyer was living in same building we had good relationship and therefore trusted her and agreed to keep 4.5 lacs pending and executed agreement with value 31.5 lacs instead of 36 lacs and buyer agreed to pay balance 4.5 lacs in Cash with in a Month from agreement date,but failed to pay even after Seven months of follow up. Buyer even made false promises and later in Jan-2017 refused to pay balance amount 4.5 lacs. Name transfer of flat blocked with legal notice. As evidence i have, MOU signed by buyer In Sep-2016 wherein she agreed to pay balance amount in 15 days. Also 28 phone calls recorded on mobile phone along with one Video recording containing her confession about unable to pay. Pls advice