While the DNC list isn't the best defence, it certainly IS effective if used properly.
In your case the callers are using phone lines provided by Level3 Communications LLC. The operators of networks today are very sensitive to users violating the law and their own TOS.
If you want the most effect, call 1.800.829.0420 or email customercare@level3.com and tell them that these people are blatantly ignoring your request not to contact you and the DNC list.
I'll bet somebody further up the food chain than the lackies calling you gets a call that starts with a sentence like "If you would like to continue hearing dial tone when you pick up your phone.......".
