Compromised credit card

When I got home from my psychology appointment (which went very well), there was a message from BMO Fraud and Investigative services asking us to call them back. Of course I called them back right away but I was confused when the thing asked for a card number because I had no idea which card or account they were referring to when they called. We have separate and joint accounts with BMO along with credit cards and I didn't want to put in the wrong card.

I explained this problem to the live person to whom I was transferred and she was able to check the account in question by looking up our names. It turned out that they were concerned about my Mastercard. They asked about a couple of transactions and I confirmed that I'd made them and then they asked if I'd bought airline tickets to Vietnam.

Airline tickets to Vietnam??? Five of them? Those were definitely not purchased by me. Eeep. Apparently after those transactions went through the company refused further transactions on the card until they talked to me. And they cancelled the card while talking to me. I'll receive a new card via courier by Tuesday afternoon.

The stolen transactions haven't appeared on the online report but if they do end up on the card, they'll be refunded in ten business days.

The bank doesn't yet know how the card information was stolen; they flagged this based on my purchasing habits. I'm very grateful to them for seeing this and contacting me as quickly as they did. I wish they knew how the card information was stolen but they have no idea. She suggested that it was probably done when I physically used my card at a merchant but I haven't brought the card out to be used since mid-June. I have made a number of online purchases since then so I wonder if the problem happened that way?

I feel a little unsettled, having my card actually compromised. I'm sure most of us have received a call telling us that a card has been compromised but nothing has really happened. To have the card number not just stolen but actually used... I feel violated, in a way, and more than a little paranoid about using the replacement card.