They have a do not call list. I know the feeling though. I have told them no and to stop calling me now they prank call me. Try recording the calls and call the company.
hahaha, sorry but it's funny in a way... i guess it's not a good idea to upset telemarketers... but yea, if you record their voice and play it back to them saying that you would complain to their manager they'd most likely leave you alone...