have you cancelled the sale agreement in writing and communicated the same to him?
If not then do it at once.
You can issue a legal notice to him stating that his presence in the house is considered to be an illegal trespass and punishable as per criminal laws.
You can demand him to vacate the illegally trespassed property immediately or to face legal consequences.
After that you can lodge a criminal complaint agaisnt him with the local police.
You can send the complaint from your place also but until and unless you follow it up closely in person you will not get the relief through police so easily.
If you are not able to pursue the matter in person you can authorise any one of your close relative i India to regularly follow and put pressure on police for taking proper legal action against him.
You can also file a suit for ejectment and permanent injunction against him to eject him from the property, recover possession and to restrain him from interfering in your possession and enjoyment of your property.