Withdraw MOU

Hello Experts, Recently we purchased a notary plot of 80 sqyards. Initially it is a 160 sqyds plot and there is a house in that plot. So we purchased 80sqyards and demolished that house in order to take our part and 80sqyards boundaries. The plot is not in a proper shape and having boundaries. All 4 boundaries are different lengths. We don't know that initially. We know only East&North corner is increased. They said as per VASTHU it is good only. So when coming to take our part of 80sqyards they denied to give the plot in proper shape. So we signed an MOU saying that in 6 months of they have to return the money. If they fails to return the money we will take over the plot as per proper shape. But now they constructed a basement in our plot without informing us and they did not gave money also. They have the time till August 19 to return the money. But now we want to take the plot based on their actions in our plot. So is it acceptable to change our decision by taking the plot . Please suggest us can we go for the plot by cancelling that agreement?