Your first mistake is adding your number to the national do not call list. That agency sells your phone number, as well as whitepages.com. AT&T laughs all the way to the bank because they provide these criminals with phone service. And our leaders in Washington are too busy to go after these crooks. They spend their time making laws on which rest rooms we should use.
There are many ways that telemaggoters obtain phone numbers. A prime example is an organization that my mother has belonged to for quite some time. They reserve the right to share information on members with third parties. The DMV is another example. Then there are those operations that use random dialers. Not to mention companies that go out of business and sell the information on their customers. The list goes on and on.