on your landline, answer the call and then press zero over and over and over and over and over and over and over and over and over and over and over and over and over and over and over and over and over and over and over and over and over...

That will mess up their automation maybe even glitch out their system. Especially if they call back. Could possibly get your number placed on their "do not call" list automatically because their computer will mark the call that it contacted a fax/computer..

Also you could record the FAX connection noise and play it to the call, that should make it mark you number as a fax/computer and they probably wont call back.