No telemarketers want to be telemarketers.
The fact of the matter is, when a call automatically gets made from their dock and the person is an asshole they just set it as a callback and the computer calls the number back at a random time, which is normally within 20 minutes, and the call is made from the dock of a random telemarketer in the office.
There could be 200 of them so if you're rude.......callback.
If you politely say 'Look, I've been called from this number so many times. Could you please take me off your list' then they'll probably remove you from their calls register and thank you for your time.