I am mystified by the feelings of some people (starting with my spouse) that one cannot simply hang up on an unsolicited caller. A phone call is an interruption in the callee’s home or business. It is rude and, generally, unwanted.
And for those of you who want to give a polite answer to a rude interruption, try this: I am sorry, but I do not give personal information to strangers over the phone, and I do not give money in response to strangers calling on the phone.
Of if you want to be a wiseguy, say: I can’t talk now, but if you give me your number, I’ll call you back when it’s convenient for me. And they never give a phone number, because they do not want to be annoyed.