I am on the do not call list as well - my advice is to report each and every call to the do not call center - they have an online form to fill out for each instance - they wont respond to one call but we get everyone else reporting them, they will react
phone companies can always block a number for a fee per month - i suggest getting on the do not call registry - you must wait 31 days before you can report a bad call the first time but after 31 days are over, you report every time they call - eventually local authorities will investigate and remove them temporarily