They left a Robo-message claiming to be the Internal Revenue Service filing a lawsuit.

This is one of the two numbers they left on the message.

This is why it is a scam... Follow me close here...
1. The Internal Revenue Service does not call and contact people.
2. The IRS will contact you by US MAIL, Nothing else, they don't send telegrams or any other third-party services.
3. We really don't need a third point here, but I will put something... So the number is not registered with a government agency. So refer back to point 2.

So don't call them back... just block the clowns that are trying to rip you off.