constantly calls

Hangs up - no message.

Highly suspicious. If really a nonprofit, caller was incompetent. Tried to get me to give VISA over phone and when I asked for mailer, hung up. Next day someone called with same number above related to Children's Cancer Fund and same spiel. When I said sure, mail me a brochure - she actually said,  ok, bye. I said, aren't you a nonprofit looking for money - aren't you going to send me a mailer for a donation - to which she replied "I don't know how to respond to that". If this is truly legitimate, their callers are not trained

Sounds like you threw they way off script with your comment

Could still be legit. But got to ask for mailer - I would be concerned about giving  giving credit card info over phone given the oddity of the call