Annoying Calls

These people keep calling our home number for some lady Ive never heard of before.  We've had this number for like 5 years and we still get calls for her.  I got fed up with it a few years ago and told the callers to stop or Id report them.  They did stop, but only for a few months.  Now they are getting more frequent again.  The callers never say who they are, and call with an unknown number.  All they do is ask to speak to a certain person, like they are friends with her or something, but you can hear other phones and people in the background, and its always someone different calling - they call often enough to be able to tell!  When I tell them the lady they are looking for is not here or I have no idea who she is, they hang up on me before i can say anything.  This morning when they called, I acted like I knew this lady and was about to hand her the phone.  I asked the caller who she was, what her number was, and told her I was writting it down.  Then I told her that I planned to report them because of thier non-stop calls.  That I dont know the woman they are seeking and have told them many times already.