The federal law mandates that anyone must stop calling if you simply ask them to add your number to their internal do not call list.
If they fail to do so, and after 30 days call they again, they're subject to federal fines and, most likely, state fines since nearly every state has it's own dnc laws.
Whenever I get a call at home from any entity that I don't want to hear from, I just politely interrupt and say, "Please add this number to your internal do not call list". Sometimes they get rude, but I shrug it off and just repeat the request.
btw: some state laws even give a cut of the fine to the person filing the complaint. Of course, now just hoppleheads are filing hundreds of bogus complaints hoping to make a little free money.