"Coming to think of it, if the charges were run up on a credit card, wouldn't the card company cover him?"
They have, they acknowledged it was fradulent and put the money back in his CC account. That means Sony now have to take the 'hit' hence the alleged debt against his account. If the £50 charge was against another user or something else (liek a phone) that would've been blocked, but because it was fradulent against HIS acocunt, he's effectively been blocked out.
I'd love to know why Sony can't just removed the service or content that was purchased and remove the debt too