Firstly you should know that
- Stamp paper has no limitation period or expiry date.
- A stamp paper can be used at any time after purchase of it,
- The Indian Stamp Act only fix a period to get the refund amount of unused stamp papers i.e. six months from the date of purchase but it does not defines any where the time period for use of stamp paper.
- According to Supreme Court judgement in the case of Thiruvengada Pillai Vs. Navaneethammal and Anr., the stamp papers do not have any expiry period.
Hence, the said stamp paper of Rs.500/- duly signed by you ,even by force , can be used by your above said guy for the nefarious purposes against you. He can use the same for the amount recovery purposes from you.
You should lodge a police complaint against him after narrating that you have nothing to do with that stamp paper but you are getting threatening call to misuse the same.
In your absence , any one of your family can lodge the same on behalf of you.