MCM harrasing calls

I've been receiving phone calls every morning from a company called MCM. They are calling for my son, who is 31 years old and is doing mission work in Chile and has been for over two years. When I tell them that, they just hang up and call again the next day. From my research I see they are a bad debt collection company, but I can't give them any more information than I have. We communicate through Facebook and email. Am I within my rights to, for instance, to blow a whistle into the phone when they call? This has nothing to do with me, my son hasn't lived here in 7 years, I work late into the night and need to sleep in the AM.

Any comments?

Thanks, Joe