In almost all cases, this is confusion caused by looking at the wrong bank statement. Please first check that you are looking at the same bank statement associated to the card originally used to make your booking.
For some bank accounts, the refund will appear as a credit alongside the original transaction, rather than as a new credit on your most recent transaction statement. We would advise checking your historic bank statements for the original payment.
Refunds issued shortly after the original charge appear in the form of a reversal instead of a refund. In the case of a reversal, the original charge drops off your statement, and a separate credit is not issued.