I missed a call from this number. I called the number back and the automated service said it was COMCAST Telemotions (or something like that) and they were calling me about a new promotion. One of the automated options was to stop receiving phone calls. I pressed that number, but was then told cancelling wasn't available. Then it asked me to leave a message. I just hung up.
By calling them back you now may get more calls. Do not answer unknown calls and never call them back. Resist the urge to call back. You get no bonus points for knowing who called you.