Numerous, harrassing sales calls

I receive sales calls from this organization at least twice weekly on my company's business cell phone. I have asked them repeatedly to put me on their Do Not Call registry. I have listed my business cell phone to the National Do Not Call Registry as well. Despite these efforts they continue to call me and tell me each time they will update my number to their Do Not Call list. It never happens as they continue to call and always from an obscure area code. I block the number each and every time but I continue to get them with different area codes.