What numbers to enter with activating account with credit card?

I am trying to activate my World of Warcraft account so I can of course, play again. I have my credit card and you have to do the three four digits but i enter it in and it says wrong transaction. What do I do? I haven't used my VISA card in awhile also.|||We have no idea what might be wrong with YOUR credit card. Call the lender.|||Is it really saying three or four digit number? If so, the number they want is most likely the verification code. On most cards, the three digit number is on the back. AMEX has the four digit number on the front.