Similar incident happened with myself a few years ago... had a mastercard that I use specifically for online purchases such as with Amazon and somehow someone used my m/c as a seller through Amazon US charging my card a few hundred dollars.
After speaking with Amazon Australia they transferred me to Amazon US where all they could confirm with me was that a seller account had charged my card several times (how on earth they got my card details I'll never know). The CBA to their credit reimbursed me in a timely manner. Going forward a verified code has to be entered to approve any charge on m/c as an additional safeguard.
I always remind my young adult kid's not to click on any text link/careful opening e-mail attachments etc. always to verify with whatever organisation it is sending you such stuff. Latest was an Auspost scam asking my son to confirm his details before proceeding with his delivery. Nowadays have to be extra careful as they try catch you off guard or being naive/complacent.
