The DNC does work, with legitimate companies, but it's not a call blocker so it can't keep scammers from calling you. Only you can do that. Invest in a real call blocker or at the very least, don't answer calls from numbers you don't recognize and don't call numbers back "just to find out who called." If they don't leave a message, they aren't worth your time.
"This is Sarah with Consumer Services calling about your credit card. There is no issue with your card. If you want to lower your interest rate, please press one to be connected with an operator." CLICK.