Tell them you're on the Telephone Preference Service - it's illegal for a telesales agents to continue to stay on the phone to you after that. At least, that's how I was trained when I worked for various telesales agencies.|
I did door-to-door sales too. One very effective way of getting rid of me was a scary looking man with two mean boxers straining at the leash to get at me. "Oh I can see you're busy I'll just move on."