Where do you think this is coming from?

My father gave me a call and said that someone located in London has been using his credit card and stole almost 3000$! He said he doesn't purchase things online and that the trouble has to be coming from one of the websites I use to buy games and I don't know much about them and I know a lot of people in steamgifts buy from them so where do you think it got stolen from?

Here are the websites I use to buy games on
G2A (my guts are telling me its from here..)
Steam (highly unlikely, almost impossible)
Greenmangaming (maybe..?)
Xbox store (same as steam)
I also used Netflix but he knows it takes 10$ a month

Has anyone else had this issue using g2a or gmg? Can this even happen in any of these websites? And no I never told anyone the credit card number or showed it to anyone all my purchases came from home