Play reverse psychology on them. Pick up the headset and say nothing. Set it down on the desk and walk away or something. Costs them money to connect and costs you nothing.

Called the number back, a live person answered, saying that the call is recorded.  Told him to remove my number from the do not call list.

The phone screen had Campbell and some letter following.  My husband answered, but no voice and a few seconds later, a hang-up.

Called and did not leave a message.