Have felt your pain on all points at one time or another. I never even knew that call centers existed until I took this position last year and have vented about them many times on this site. Have told some repeatedly not to call back and been ignored. I've heard that call blocking must be done through your service provider. Unfortunately, these places either change numbers frequently or spoof a legitimate business, so it would be difficult to keep up. What's strange is that any time I pick up the receiver for this number, there's never a person on the line, just an ear-piercing tone.
This # calls 3 or 4 times per day. It is so annoying to hurry to the phone, say hello and it is silent. Sometimes they just hang up and other times they ask for the owner or president. They are so persistent and for what reason I do not know. Wish I could just block them. Hope I can remember to ask them to add me to their "do not call" list.
UPDATE: Have now received several "live" calls from an industry-specific magazine at this number (Caller ID). The reps ask to speak with various members of management regarding changes to their subscriptions. However, they say to call back 208-281-3100, for which there is no record on the Internet. One executive admin confirmed that her supervisor has a free subscription but doesn't wish to talk to them.