Try a call blocking device, blocking the number, or simply ignoring it all ways possible, including shutting down any answering machine. If you're answering in any way, they will keep calling.
These people call relentlessly from various numbers. Stating they represent Hylan Industries (sp). They have been told each time to stop calling. Our number is on the do not call register.
Woman said she was from global ecchange. I asked to be taken off their call list and she directed me to the "supervisor". They call from different numbers