If they call you on your cell phone (I use an Andriod), you can go to your call log, click on their number, then click on settings and add them to the Reject List. Your cell phone will automatically hang up on the call.
11 calls in under 30 minutes! I called them back and told them to take me off the call list as this is ridiculous. The woman was nice enough and said she would take it off. Not even two minutes after I hangup with her, I get yet another call.