When I get these calls (assuming I get a "live" person), I always ask them to remove our number from their calling list. Tele-marketers and charities are required to do this if you ask them, and they are allowed only one "mistake" after you ask. If you document the calls after you request to be taken off their list and they exceed that, apparently it's pretty easy to file a claim with the government; the caller gets fined and you get the money (I think over $100).
I've had a couple of charities that couldn't get it right (I suspect volunteer callers) and had to ask several times, but they all eventually have stopped calling. There's no need to be nasty on the phone, either. I am very polite when I ask. Most companies have trained their callers to respond appropriately.
It's well worth taking the time to answer the phone and make this request. The phone rings so much less frequently now!!!