So they (Airbnb?) cancelled a reservation for your place 2 days before arrival that was for 3 months? They haven't given the guest an explanation and consequently intent not to pay you?
If those are the facts there has to be a logical explanation because Airbnb is not in business to lose money nor to play mystery games for fun. The first thing *I* would want to know why it was cancelled since that would effect me getting paid or not, before worrying that the guest didn't get an explanation. Their answer may explain everything.