Credit card fraud used online...any advice?

Fingerbobs

I have an old Marbles card, which I have not used for about 3 or 4 years. A few months back, I was surprised to receive a statement with two fraudulent transactions on it.

They must just try random numbers until they hit on a "valid" one - there's no way they could have "intercepted" anything I did with that card because I simply had not used it for anything for years.

It wasn't an issue - Marbles instantly blocked the card, made me complete a form, sign it to confirm that I did not authorise the offending transactions, and send it back. They then refunded the money and sent me a new card with a new number, and I haven't heard any more about it.

All pretty straightforward really.