These people are like viruses. Turn it around on them - send faxes to the number that called you to tie up their lines and drive them crazy. you won't get charged for it, 'cause it won't go through, but they'll get that annoying squeal if they answer.
The ever famous female voice robo call with "an urgent public service announcement concerning your energy bill" saying there's a "US renewable energy plan" to "avoid the coming 14% rate increase". If you're a homeowner and pay more than $150 a month in electricity press 1. "If we have reached you in error and want to be taken off the list, press 3". SCUM. Caller ID read Teaneck, NJ.
Reported their DNC violation to the FTC, however useless and futile that is: https://complaints.donotcall.gov/complaint/complaintcheck.aspx?panel=2