No x 3

Lately I have been getting a lot of solicitor phone calls. When I see the 866 or 877 number I know that it is not a call I want. I always try to start off polite because the person at the other end is just trying to do their job and make a living. What I do not understand is when I say "no" once, why can't they accept it. They go on and on and I say "no" twice. I do not really want to hang up on someone, but if I have to say "no" the third time, I hang up. The next time someone does not take my first "no" as the end of the conversation, I am going to ask them to explain why they want to continue the call until someone is forced to be rude.