Cancelleation of agreement of sale

I want to cancel and request the money which I paid to seller. Agreement made on 100 rs bond paper. Banker have that copy for loan purchase. Reason for cancellation: I came to know that Revenue department mentioned that land belongs to Govt case some case is there. When I check sale deed it was clear and purchased and made a gated community. Below are terms mentioned in Agreement: 1. The Sale consideration of the Schedule Property is fixed at Rs. 3200000 (Rupees only). 2. The PURCHASER has paid a sum of Rs. 200000 (Two Lakhs Rupees only) by cash as advance, the receipt of which sum the SELLER hereby acknowledges. 3. The balance payment of Rs . 3000000 (Thirty Lakhs Rupees only) will be paid by the PURCHASER to the SELLER at the time of execution of the absolute Sale Deed and thus completing the Sale transaction. 4. The parties herein covenant to complete the Sale transaction and to execute the Absolute Sale Deed by the end of ____________________ 5. The SELLER confirms with the PURCHASER that he/she has not entered into any agreement for sale, mortgage or exchange whatsoever with any other person relating to the Schedule Property of this Agreement. 6. The SELLER hereby assures the PURCHASER and he/she has absolute power to convey the same and there are no encumbrances, liens, charges, Government dues, attachments, acquisition, or requisition, proceedings etc. 7. The SELLER agrees to put the purchaser in absolute and vacant possession of the schedule property after executing the sale deed and registering the same in the jurisdictional Sub-Registrar's office. 8. The SELLER covenants with the purchaser that he/she shall not do any act, deed or thing creating any charge, lien or encumbrance in respect of the schedule property during the subsistence of this Agreement. 9. The SELLER has specifically agreed and covenants with the PURCHASER that he/she shall do all acts, deeds and things which are necessary and requisite to convey absolute and marketable title in respect of the schedule property in favour of the PURCHASER or his nominee. 10. IT IS AGREED between the parties that all expenses towards Stamp Duty and Registration charges shall be borne by the PURCHASER only. 11. The PURCHASER shall have the right to nominate or assign his right under this Agreement to any person / persons of his choice and the SELLER shall execute the Sale Deed as per terms and conditions of this Agreement in favor of the PURCHASER or his nominee or assignee. 12. The SELLER has agreed to get consent deed duly executed to this Sale transaction from his wife/her husband, sons and daughters on or before date of registration of Sale Deed and assured that they all join to execute sale deed in favor of the purchaser. 13. It is hereby expressly provided and agreed by the parties here to that both parties are entitled to enforce specific performance of the agreement against each other in case of breach of any conditions mentioned in this Agreement. Please suggest what is the best way to cancel and ask the money to return which I paid.