The best way to mess with these people is tell them you'll donate so have them send you a bill then send it back with no money and write on the bill to take you off their list. They get no money and it cost them postage.
I've been getting phone calls from this organization for more than a year. One time I did pick up, stupid me, and listened to their speech. I told them I was not interested and hung up. They've started calling again recently. ANNOYING!!!