Picture this: you lost your credit card, and a transaction (which you didn’t initiate) takes place. Will you still be liable to pay that amount even if you have reported the card to be lost/stolen? Well, it depends. The answer lies in how long you took to flag the unauthorised transaction.
It goes without saying that the first thing that any user should do if they lose their credit card is to block it before anyone uses it, so there's nothing to owe. Even if you are not sure if the card is stolen or lost, freeze it. Every bank lets users switch card transactions off and back on.