Report the scammers online to the FBI at their Internet Crime Complaint Center, which is at IC3.gov. They are committing fraud and if found can be prosecuted.
As far as stopping them, you probably can't. They are calling from outside of the country and they cannot be stopped by the Do Not Call register. Nor do they care about any threats of legal action. You're not going to be able to find them and they know it. But you can slow them down.
The best way to get rid of them is not to answer phone calls from numbers that you do not recognize. Then block those numbers. Also, ignore any phone message or email from someone you don't know who has news that's too good to be true. They are always scams. Block those too.
These scammers make calls and send out emails by the thousands and only know that their call or email got a live fish on their hook if you bother to call or email them back. Once they know they reached a live person, you'll get more and more scam offers.
However, if you don't make actual contact with them at all, the number of these calls or emails that you get will be drastically reduced.
Just checking in to see if you need more help or any clarification of my answer. If so, please reply here on this question thread.