Robo-call, final warning, IRS is suing me. Report IRS impersonation scams to the Department of the Treasury, https://www.treasury.gov/tigta/contact_report_scam.shtml. Also make a report with the FCC. It's hard to know if these reports help, but if any little bit of information helps catch them, or make the charges against them greater when they do get caught, then it's worth the 2 minutes to fill out the online form.