called at 1pm on a wednesday. I answered, there was not a sound on the other line.

Called my cell and left no message. Only 3 family members have my cell #.  What good is a federal & state DO NOT CALL list if no one enforces these laws and violators are never punished?

Got a call from this number, but they didn't leave a message. Called using my work land-line phone to see who picks up, but there was no sound, not even a ring. I hung up after 30 seconds into the call.

I got a call from this number, no message.

Many companies use a circuit known as a PRI (primary rate ISDN).  It's like a T-1, except that rather than 24 talk paths, it has 23, plus one data channel.  The data channel can collect inbound Caller ID and a bunch of other information, but it can also be used to display any phone number (Caller ID) on outbound calls.  Companies that are legitimate will display their own phone number, or that of their main (advertised) telephone number.  Those using a PRI for 'evil' will display a phone number they don't own in hopes of a called party answering.  It you try to turn them in, you'll only be turning in a company who has had their phone number spoofed.  It's not Verizon's fault.  If you're getting a robo-call, it's probably being done with a Voice Response Unit connected to high capacity phone lines (like a PRI or a bundle of PRI's).