Same issue. They called me with a name I had 10 years ago and asked for my last four. When I asked who was calling she said SHE had to verify who she was talking to. And now she can go u know what herself...go harass someone else who actually owes!
On the new OS of the iPhones if you click the little i to the right of the number it takes you to a new screen and if you scroll to the bottom you can block the call. I am so sick of these people failing to comply with the statute of limitations and selling the debt thinking the clock starts over, WRONG. Also, this is a great thing to do to telemarketers and collection agencies, just did it myself today. Click on this youtube link called INTERRUPTING TELEMARKETERS (PHONE PRANK)
to watch this guy in action Hilarious http://youtu.be/RVKyUFI1b1c