I understand where you're coming from. If someone does want to donate to a charity, make sure you do it as anonymously as possible! Never provide any kind of legitimate contact information or they will hound you like a swarm of mosquitoes.
I ran into this problem with Habitat for Humanity. Before Caller ID and when answering machines recorded on tape, a caller would call every day at about the same time and hang up at a point where my answering machine would run the tape to the end with nothing on it, preventing any legitimate callers from leaving a message. One day I was home from work early and at the time of the mystery calls the phone rang - it was Habitat for Humanity who I had donated to just a couple of weeks earlier. I made it clear that their calls were unwelcome, and lo and behold the "mystery calls" stopped.
NEVER give any charity your contact information! They will hound you day in and day out!
oh, on another note, this place can't be legit...they are not even listed in www.superpages.com (either white or yellow pages). any legitimate organization would be listed and they would answer their phone. Do not answer your phone, they most likely have some sort of tricky spam deal going on or worst yet record your voice for whatever devious reasons. You'd be surprise what technology can do now...I know I'm an internet marketer (but I'm "white hat", meaning good).