@Anikó7
Very vague post; did you contact guest? did guest reply? at booking, you should have guests cell phone number,..did you call them? Did you message AirBnB customer service?
Any 'review' that they leave will undoubtedly get removed from the site,...because they didn't stay there. Not allowed by policy to leave a review on a property they didn't stay at.
If your refund policy is set to "FIRM" then they are not entitled to any refund.