someone has used my card to purchase music and other items

I am hoping that you can stop this, if I have to I will go through my bank and stop it by getting rid of my card and changing my account also if I need to I will donate this computer and get rid of my I phone. How did they access my credit card I believe it was with my iPhone but then again it could have been my computer

I have purchases some has purchased music using my credit card 1403, card in which I have on file in my apple account. I have never downloaded any music