How to revoke Sale Agreement and POA?

I have entered a sale agreement in the year 2018 for the sale of a plot of land in Assam. The purchaser also took a power of attorney where it was mentioned that he can totally manage the property. It was orally decided that he would leave 7 ft. land as way to the landowners (my relatives) behind the land but later he said the he will only leave 3ft. land. My relatives called me and we decided to put posts in the land excluding the 7ft. distance, after some time the purchaser called me and scolded me and uprooted the posts. Now, I don\'t want to sell the land to this person anymore even if he decides to leave 7ft. of land. I took more than half of the total payment on grounds of necessity which was mentioned in the agreement. The sale agreement was only notarized. As almost 6 years had passed is the agreement still valid? If yes, is it revocable? Also there was a minor mistake in the agreement regarding the location of the land. The name of village was wrong. How to the revoke POA?