We have gotten a few calls from this number.  After seeing on here that they have an option to be removed from the records, I called back and got a recorded message asking me to press 1 if I wanted someone to contact me and 2 if I wanted to be removed from their records.  I pressed 2 and the call was immediately disconnected.  I'm guessing it didn't really remove our number and that they'll claim that there was some kind of system problem.

Called many times without leaving a message. I finally answered, and they claimed to be Timeshare Advocacy Group, said they were not buying or selling timeshares but wanted me to come to an "information meeting" on how to reduce my cost for next year. The meeting was at a local cafe, they were paying for dinner. I chose not to go. They asked if they could call me next year when they were in town. I'll see what else I can find on them.

They keep calling several times a day and never leave a message.

A call-blocker. See my post on whocallsme under 3059182338 to find out how to get one.

Unsolicited call.  what is the fastest legal way to get them to StoP?

I received a call from this number that I did not get a response when I answered the phone and asked who do I know in Antioch.

I had the same experience, the phone just range three times and no voicemail was left.  We are on the do-not-call list, but still get a lot of phone solicitation.

they have called me several times also, and the phone only rings 2-3 times--not enough to go to voicemail. Thank goodness for caller ID--it only show the number and Antioch, CA, but I know I don't know anyone there.

This company calls every day between 3 and 5pm (EST). Just let call go to voice mail which they never left a message. When I called the number back 925-529-8446, they claim to be:
Timeshare Advocacy Group

They use several numbers to call from the area code 925.

I have never owned a Timeshare, and do not plan to in the future.

They have an option to remove your number from the records. Don't know if its working yet.