Get a lifeguard whistle and when you recognize this same number again and again, pick up the phone and blow as hard as you can. Even if they don't quit calling, you will get enormous satisfaction!
To report the fraud, go here:
http://www.grants.gov/web/grants/support/general-support/grant-fraud.html
Their number is listed , along with an email address, at the top of the page.
Also here:
http://www.consumer.ftc.gov/articles/0113-government-grant-scams