David, as much as it pains me to say it, you may not have been incorectly penalised. Firstly, you've been a little spartan on detail, but reading between the lines, I assume this is what has occured:
1. You accepted a reservation, in good faith, either by approving the booking request, or enabling the Instant Book option.
2. You re-evaluated your circumstances, and cancelled the guest's reservation, which incurs censure, not least of which is that host cancellation is an infraction which entitles Airbnb to block off your clanedar, fine you, and/or suspend your eligibility for superhost status.
A host simply cannot make amendments on a whim, unless under duress or extentuating circumstances (which are limited to serious instances - "changing my holiday plans" most certainly doesn't constitute said circumstances.) This has consequences. For you, the guest and the company (namely Airbnb, who bear the expense of refunding your guest in full, with bonus reparations, and dedicating customer service assistance to re-host the guest you cancelled at company expense.)
If my assessment is incorrect, I apologise i advance. But if I am correct, I highly doubt you'll receive any remedy from Airbnb.
