The scammer asked for my credit card number and I gave it to him. What do I do?
This is simple. You need to immediately, like right now, contact the company (Visa, MC, American Express, JCB etc.) that issued the credit card. They all have local numbers or toll free numbers you can call. The number should be on the back of the card. You need to do this because the scammers are going to start using your card to charge things with. You don't want to be responsible for that. It's the same thing as a lost or stolen credit card. In this case, it's stolen, although you still have the card.
If you don't, the scammer can charge up to your credit card limit. As an example, let's says you have a zero balance and a $1,000 limit. The scammer can charge up to $1,000 and you're going to be responsible to pay the card company. That means you are going to pay $1,000 plus any interest payments. So the scammer has just stolen $1,000+ from you. Not a lot of fun. Not to mention that it can ruin your credit rating. Wow, if you had like a gold card, think of the fun the scammer could have with that. You won't have any fun but the criminal will.
Getting a new credit card is not a lot of fun, but it's better than the alternative. And in the future, please don't give out your credit card information to someone on the internet that you don't know or trust.
"If the law can do nothing we must take the risk ourselves...I am not the law but I represent justice..."- Sherlock Holmes