@Sher1100 The guest cancelled the booking from their end, or you cancelled it? If you got a message from Airbnb saying the guest wants to cancel and asking you to accept it, that gets registered as a host cancellation, with all the penalties applied, one of which is blocking your calendar. If you ever get a message like that, decline it. The guest can cancel easily from their side without involving the host- those messages are a tricky way for a guest to get a full refund.
Try contacting Airbnb through their messaging function or their Twitter account- the phone lines have ridiculous wait times right now. It may take awhile to get a response, but at least you won't be wasting time holding the phone.