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!
I donated to the local Cancer Soc. in memory of a sister-in-law. I told them it was a once and done donation and I did not want to be bothered any more. I keep getting calls and either hang up on them or just push the answer button and hang up right away. From now on I will just let it ring as another party suggested.
I get those calls all the time but I don't answer it, I let my answer machine pick up and of course they don't leave a message. I'm on DO NOT CALL list and I thought it's supposed stop them from calling us. I guess not. What is a point to be on the list if they don't enforce it. This is very annoying of getting calls that I don't recognize the number. There must be a way to stop them from calling us once and for all.