Robo calls go down a list, i.e. xxx-xxx-0001, xxx-xxx-0002, so they don't need to buy your number from anyone. They really don't care about the Do Not call list because in order for them to be fined they know that you have to answer their call, tell them that you're on the list and thereafter keep a record of every time they call.
I get multiple calls a day from various spammers disguising themselves as telemarketers. I'm on the DNC-it doesn't work with criminals, just as gun control and speeding laws don't stop curmudgeons. Enough complaints have been made about these pests that finally legislation is being enacted. Normally I don't like big gov't but this is one exception.
Please check the following websites and encourage your senators and representatives to support this legislation and chase these offending culprits back under their rock!
Senator Chuck Schumer has introduced the Robocop Act that will require phone companies to provide consumers with blocking technology.
http://consumersunion.org/campaign-updates/se ... -to-the-senate/
https://www.schumer.senate.gov/newsroom/press ... le-to-consumers
Representative Jackie Speier (CA) introduced HR4932 ROBOCOP act to House of Representatives https://www.congress.gov/bill/114th-congress/house-bill/4932