Guest arrived and next day check out but airbnb refund automatically.

[Vincent98]

I never cancel the reservation but why airbnb told me I  canceled and refund？

[Linda108]

@Vincent98  Did you get a confirmation of a reservation?  I don't see that you have a the automated concellation review which would be an indication you cancelled.  Sometimes during the booking process, Air BNB will cancel the reservation before it is completed and it will show up on your Reservations as cancelled.  I have had the same thing happen to me.  There are no consequences for the cancellation - no money, no blocked days.