NRI property purchased on Power of Authority (POA)

Dear Law Experts, I bought a property in Bangalore in May 2006 on behalf of an NRI using a General POA which does not allow me to sell the property. (I dont know if he had to go through any procedures with RBI or any govt office) which was registered in the Registrar’s office with this POA which was neither notarized nor registered with any authority. The NRI failed to pay the agents / dealers their due commissions which was agreed on his behalf. I paid it from my pocket. I gave him only the duplicate sales deed and held back with me the original SALE deed. The NRI wanted to sell the property but realized the duplicate sale deed was lost by him. He asked me for the Original but I refused. Subsequently he issued a notice at a website as below: Quote “ GPA Executed by XXXXXXXX in favour of yyyyyyyy stands terminated with immediate effect 28 Jan 2010 This is to inform that, the GPA Executed by my client Sri xxxxxxxx in favour of Sri. yyyyyyyyy stands terminated with immediate effect. The General Public is called upon not to deal with yyyyyyy herein afterwards in respect to “COMPANY NAME” and property bearing Sy. No. zzzzzzzzzz , Bangalore . Kindly note my client shall not be responsible for any act done by yyyyyyyy “ Unquote. The NRI made a police complaint that his original Sale Deed was lost and he was therefore applying for an additional copy with the Registrar’s office. I was not informed about any such notice either by the NRI or his lawyer and I was also not informed about the complaint of lost Original sale deed. The local address for the NRI as mentioned in the Sale Deed was my house address. My question is : How do I stop the NRI from selling the property and ask him to pay my losses. Can I issue a Public Notice asking the public not to buy the property for any valid reason? What could be a Valid Reason?