Make it simple! NEVER , EVER answer a call from a number you do not recognize. If it's important- the caller will leave a message. These SCUMBAGS will NEVER, EVER leave a message!
Got a call from this phone number and didn't pick the call. I call the number back and a very sloppy noisy clumsy sound recorder mentioned "To be eliminated from our call list press 1". I hang-up.
Received a call from 650-262-1122 at 5 pm. Did not leave a message. I called the number and the message (barely audible) said "push any number to have my phone number removed from their list. It will take 24-48 hours".