Every successful effort to reduce robocalling has been the result of an enforcement action. On October 4, 2016, local police in Thane India raided six criminal call centers. IRS impersonation calls to the US declined 85% the next day.
Source: IRS Office of Fraud Detection and Prevention
When IRS impersonation complaints began to increase in June and July 2017, most of the increase was tied to phone numbers activated by individuals associated with the criminal group that had been raided the previous October.
The October 2016 raids also resulted in a significant drop in overall robocalling complaints.
Source: FTC.gov