Not much - they're scammers calling from overseas.  Best you can do is block their number(s) or assign a no-ring tone which means you won't hear the phone ringing, and it'll just go directly to voice mail.  You can tell them you know they're scammers, you've reported them, and you definitely won't pay them.  If you're getting these calls at work, please print up this thread and give to your HR Dept and/or manager to alert them you're being harassed by scammers.