First of all it is not clear that how did yo buy the property and also get khata as well as the taxes paid on yor name.
You have not purchased the property by a registered sale deed.
It was only a GPA and the sale agreement.
Both can be cancelled by the land owner at any moment.
In fact the sale agreement cannot be enforced since it is barred by limitation (3 years from the date of agreement), even if it was a registered deed.
However you can issue a legal notice to the land owner instructing him to execute a registered sale deed in yor favor on the basis of the sale agreement or you can execute a registered sale deed in favor of any of your close relative on the basis of GPA deed in your name.
But for this the GPA deed should be a registered deed.
You can consult a local lawyer on the basis of relevant papers in your possession and take his further advice on next move about this.