You may or may not have registered your new secret number with the DNC registry.
Suppose you did. If the DNC registry worked, then there is no need for your secret number. If it doesn't work, then there is a chance they can find you - for example, random dialing.
Suppose you did not register. A spammer can always work through all the numbers between two consecutive registered numbers.
Whichever way, no guarantee of zero spam. But if you did register, you at least technically can take action against the spammer.