These guys are telemarketers making illegal calls. They "spoof" the Caller ID information that we see in an effort to make it harder for them to be caught. They claim they can lower your credit card interest rates. They cannot. They are "phishing" for your personal information -- especially your credit card numbers. Tell them nothing, not even your name. Nada. Zero. Zilch.
If you press a number to speak to a real person, they will only laugh at you and hang up. Some will even curse at you and will call you back more often. It may feel satisfying to blow a whistle into their eardrum, but you are only asking for trouble. Just don't speak to them in the first place.
Some phones or phone companies will allow you to block numbers that are harassing you. If that doesn't work, you can should them to your phone's address book under SCAM or DO NOT ANSWER.
And, last but certainly not least, immediately report ALL of these scam calls to www.donotcall.gov.
I'm glad to see so many people know that these calls are from crooks. And that's why the Do Not Call law is ineffective--They're CROOKS! Block the number, let it go to voice mail or whatever, but do not engage them in any way at all.