America’s telecommunications watchdogs have levied hefty financial penalties against illegal robocallers and demanded that bad actors repay millions to their victims. But years later, little money has been collected.

Since 2015, the Federal Communications Commission has ordered violators of the Telephone Consumer Protection Act, a law governing telemarketing and robodialing, to pay $208.4 million. That sum includes so-called forfeiture orders in cases involving robocalling, Do Not Call Registry and telephone solicitation...