someone once used my card number to pay her house insurance. It can't have been deliberate fraud as of course everyone knew who she was and where she lived. It sounds more likely that someone took the card number down wrongly over the phone and didn't carry out the standard authorisation checks. Anyway, I got all the money back but had to get a new card.
I've also had calls from the card people a couple of times querying things I've supposedly bought - each time they were right, it wasn't me, it was someone in NY; I think those were genuine frauds.
But in none of these cases was my actual card involved (I hadn't been to NY or dealt with Churchill insurance). It was just someone, by accident or design, presenting my card number