Years ago, I had problems with a FAX spammer who would send junk every night. We had to leave it on overnight because it was a transport company and we would receive bills of lading at all hours. This also meant, however, that we had a separate phone line for voice calls, which did *not* need to be left free all night.
Anyhow, all of these faxes had a removal number to call, which made you jump through all sorts of hoops. I noticed shortly after attempting it that it actually *increased* the volume of spam to TWO a night. The "removal" number was, however, toll-free. This gave me an idea.
I listened and noted the timing of prompts, and the associated menu options, for the "removal" service. I brought in an old modem from home, and set it up to autodial their number (on their dime) and start "removal" processes. This I did in two different ways:
(1) First my modem would call them and demand removal of a number. They were so helpful and asked if I wished to remove another, so of course my modem would say YES, and proceed to "remove" the next number in sequence. It would cycle through all 1000 numbers in a block before disconnecting, and each time it did this, it incremented the number of the block being removed (except for invalid ones like 555). This took about four hours, all of which they had to pay the charges for. Not long after (and possibly as a direct consequence), they started limiting the calls to three numbers before hanging up.
(2) My second iteration of the program would select a random number, go through the "removal" steps, but then when asked "are you sure?" it would hit the button for "NO", at which point the process would start again. It would pick a new random number and do this again and again. If the call was terminated, it waited five minutes and called again. Since it never completed the process, the three-number limit did not apply. I think this worked for three or four days before they implemented a fifteen minute cutoff regardless of what you were doing at the time. I didn't re-program for this at all, I just tolerated the 25% loss of efficiency at driving up heir phone bill and let it call back five minutes after being disconnected.
Finally I got an angry call, during business hours, demanding that I stop doing this. I flat out said "sue me." The person at the other end finally said "why would you want me to do that?", to which I responded "because then I'll know exactly who you are, and can sue you for each of the hundreds of faxes you have sent, which I have been keeping as evidence." He coughed and said "Look, just stop calling us, eh? Nobody else can call when you're doing this." (Did I mention they were in Vancouver?) I just said "I will cease the calls as long as you do."
We got another one two weeks later, but I could only run the auto-dialer at night, so I couldn't do anything right at that moment. I got a VOICE call fifteen minutes later telling me to please disregard and not start the remove-bot again. That was the last time I heard from them.