Please Help - Getting spam called / harassed by unknown numbers

[RoosTa]

Are you sure all Unknown Numbers are spam?

If I answer it, its usually a recorded message or silence. Lots of these places have auto-dialers and transfer the calls to available operators. Sometimes the message starts to play as soon as you say "hello". Now its seems these automated systems also knows when call was declined and phones you back after 6mins. - I know this, because when I did answer the call, it stopped dialing me.

Answer the phone then just leave the phone on your desk indefinitely until you cause them to go bankrupt

I wish