Take action against IRS impostors (phone scammers)

I've never heard of IRS impostors scamming people over the phone until it happened to us. My family was scammed by IRS importers, resulting to us having to pay them for "bond" of about $29,000 (refunded once found innocent). They threatened my dad to send the money immediately or they were going to send the police to arrest him. To prove their point they called from our local police station's phone number, later did we find out that they can make any number show up on caller ID. These people are still calling us because they know that they're not getting caught. FBI says that they're not taking the case because it doesn't involve enough money but $29,000 is a lot lost for an average family. We've now been hearing that many others have been victims as well. They might not even be in the US.