I got another phonecall informing me that I had told them months ago to try me again at a later date. This time it was a woman. I told her that I didn't wish to donate, and would like to be taken off their list. She said "No problem, I can do that right now for you. Have a good evening."
I really wish I had said that sooner. Thanks to Lyricmaniac for giving me the advice to say that. Not that I should have had to have had advice in the first place. Sometimes, common sense is not my strong point... :P
Glad it's finally sorted, and just thought I'd give you all an update on it.