''Even when I hang up''?! How is that the same as actually saying ''Add this number to your Do Not Call list''? The Do Not Call registry, what I presume you mean by ''no call'', does not exist to vaguely ''take care of this''. It provides opt-out from sales callers, which comments elsewhere indicate are NOT using this number.
Here is the FTC FAQ page which the DNC site repeatedly invited you all to read before you registered your numbers. See items 28 through 32.
Q&A: The National Do Not Call Registry