Yes, they do need the DNC llst if they are a telemarketer as per the definition of a telemarketer.  They need to scrum their lists.  No, they don't buy the list to have "good" phone numbers.  That is simply some fantasy someone made up (probably a telemarketer).  It doesn't matter where they get your number, the law is the law and real legitimate companies abide by it.  Crooks and criminals never do.

DNC Complaints:
https://complaints.donotcall.gov/complaint/complaintcheck.aspx

Also file a complaint with your State Attorney General's office.
List of State AG’s offices:  http://800notes.com/faq/attorney-general

Use this web site to find an attorney in your state that will probably take the case on a contingency basis (no money out of your pocket up front):  http://www.consumeradvocates.org/

What the Do Not Call lists covers and doesn’t cover and why:  https://www.consumer.ftc.gov/articles/0108-national-do-not-call-registry

https://www.merriam-webster.com/dictionary/telemarketing
telemarketing
play
noun tele·mar·ket·ing \ˌte-lə-ˈmär-kə-tiŋ\
Definition of telemarketing
1.    :  the marketing of goods or services by telephone
telemarketer
play \-tər\ noun