Hundreds of free apps available for Smart phone users, that allow you to fake your outgoing caller id info.
5 years ago this wasn't very easy to do. Today anyone with access to the Apple ITunes Store or Google Play store can do it and have it set up in minutes.
If you get a lot of them, then report it at the FTC Website. Normally this is fraudster, scammers, Political Activist Campaigns, telemarketers and Debt Collectors.
It's an illegal practice from what I understand so you can file a complaint. visit ftc.gov/complaint, click on the FTC Complaint Assistant icon, and answer the questions.
Also do the same at the FCC website
