Hey Flux,
We also had heaps of problems with them before we signed into the do not call thingo.
I used to answer the phone and act really interested in their product and then just say "Hang on just a minute, I'll just grab a pen", then give the phone to the baby to play with for 5 minutes, every 5 minutes or so I'd go grab the phone and say "Are you still there? Sorry, can't find one, I'll just be another minute", then go off again for a while. <repeat>
It's amazing how long they will hold on the phone.

Eventually I just hang up without saying another word. It's hilarious fun! Give it a go.
Good luck,