Discovering an unknown card transaction on your bank statement can be worrying. This could be due to an error, a recurring charge you forgot, or fraud. Regardless of the origin, it's important to act quickly to protect your account. The first step is to identify the transaction. If you don't recognize it, contact your bank to report the suspicious transaction. They will be able to help you cancel it and take the necessary steps to prevent other unknown operations in the future. Don't forget to check your statement regularly to detect any discrepancies.