Wear Them Out!

Forget technology and Blocking. Anything you come up with they will work around. WEAR THEM OUT! All of these calls instruct to Press 1 now. DO IT! Tell everyone to Dial 1 and then lay the phone aside for a few minutes. This will jam the caller's lines and the 'sales people' will spend their days answering one dead line after another.
It's easy and it won't take long with no sales for the business to dry up and go away. We win!