You have to tell them to put your phone number on their internal do-not-call list.
That is because if you are removed from an existing call list, when they get a new list of numbers to begin calling,
your number might be in that new list.
If the caller refuses, challenges, or hangs up too quickly, that's a sign of an illegitimate "charity" or outright fraud.
These scammers will not have an internal do-not-call list, but they do keep an internal sucker list of phone numbers they think will be answered by gullible people.