After giving it some thought, I came up with a really good way to get back at these people! If they're calling on your cell here's what you do. First store all their numbers under DON'T ANSWER. The numbers they've used in the past are below (I'm sure there's more too).
Once you've done that, you can set that name to SILENT on most cell phones so you don't hear it ring. Others have suggested that so nothing new there. Now for the good part!
Most cell companies include No Answer Transfer in their plans. With Verizon you punch in *71. So set the number to ICS Systems main phone number (the one they DON'T use to harass people). Now then you punch in *716-514-816409 (their number), all calls you don't answer go back to them. Just make sure you answer it if it's a friend or business or their calls are going to ICS! To deactivate (on Verizon), you punch in *73. When IC Systems calls you and you don't answer it, their harassing call gets sent right to their main phone line. They don't know who's sending it since if they have caller ID on the main line, it will show THEIR OWN phone number!!
Payback is a B*tch!!