If the caller is working (not sure why you have it in italics) for a telemarketing firm I still see no reason to allow them to badger you to the point where you want to wrap the phone cord around their neck, even if they are calling for tzedaka. If a sales person in a store badgered you, you would walk out, you have every right to hang up on a person who badgers you. The problem is all tzedaka calls and callers have gotten a bad rap because of a few bad apples.
If you DO feel you are being badgered, call the organization they called for and let them know.