800-968-3504

They won't take 'not interested' as an answer.

One method is to block the number, so they can't call from it.
Another method is to put the phone down and watch TV or listen to some music until you hear that familiar "hang up sound".
or..this is my favorite...just hang up on them! I Answer, then hang up immediately without talking to them.

"I can't think of any way to make them stop."  Have you taken advantage of this new invention called the internet?  For instance did you do a search for ways to stop calls?  Did you do a search for where to report calls?  Have you looked this company up and sent them a letter telling them to stop calling you (certified, return receipt)?  Have you contacted an attorney to sue them?