Same thing happened to me with Nationwide a cople of years ago. I didn't lose a penny but neither did I everknow what had happened.
The touble was I was about to go on holiday and they'd put a stop on all my cards until they'd sent new ones, I had a right game sorting it all out ont he wa to the airport!
I hadn't and have not since used any of my cards anywhere other than a Nationwide branch, a major supermarket or a secure website. I use cash for all local purchases and at garages and restaurants.
I understand how your father feels especially as he hasn't used his card at all, but I'm told the fraudsters use computer programmes to process random numbers until they hit upon a combination whihc is actually a real card number. They are often abroad and this time they hit on his.
It happened to my sister the following week -different surnames, different banks, but has never happened to either of us since - touch wood.
Try not o feel guilty, you've not cause this. Its happening all around us but for obvious reasons the banks are not giving it too much publicity.