I have the same issue with telemarketers. They just don't listen. I had to keep blocking new phone numbers to stop them from calling again. At times when I'm not too busy at all and I feel like pulling jokes, I do the tips I found online to annoy them. Sure works well! I can't help but laugh when the caller start sighing with frustration. Hahaha!
I got the tips from http://www.callercenter.com/articles/14waystoannoytelemarketers.html and you guys should try them, too! Sure are hilarious!