>They are driving me insane.

When I get insane, I don't even try to drive. I get someone sane to do that for me. So they are actually doing you a service :).

As for the way... check how your phones work. Over here, if the recipient of the call doesn't hang up, the line would stay blocked indefinitely, until they try to call someone, or someone at the switchboard notices that it's connected for far too long, whichever comes first. Nowadays, they have some gadget which detects silence - if there's more than n minutes of it, it hangs up for you.

Now if it works like that (which you can check by calling yourself from line A to line B, then hanging up on line A and trying to make another call from it, while still not hanging up on line B), you can place your phone next to your TV so it doesn't get any silence. Good luck, and if this works, spread the word.

I already tell people around here to do that to telemarketers. Your line may be blocked for a while, but you're holding them paralyzed and they can't call anyone else for the duration.