[Kamikaze Chinchilla]

They probably meant that the hackers put a program on your computer that asked for a payment via credit card. Kind of like those email scams where they send you to a phishing site where they ask you for personal info, and once you do that, you're done. It was a good thing you didn't send them your credit card number, otherwise they probably would have had a joy ride with it and you'd have a bigger headache than you do now.

Though you might still be able to recover some of your files. When you reinstall your system, sometimes the file data will still be on there (like traces of it), even when it's not visible to you. You just need to download a data recovery program that will recover the files for you. But the old files that reside in the sector that you install the program on or save new files on will be lost.