Unfortunately, @Anna-and-Peter1, you committed an error, which happens occasionnaly to newer hosts. The guest didnot cancel himself, but sent you an invitation, that you cancel. (No idea, why such a crazy feature even exists). The system treats you with all the penalties, that you encour, if you cancel on your own.
In such cases, you better refuse the invitation and tell the guest to either cancel himself, or he will not get access, if more people show up, and pay nevertheless. If you offered refund, you can grant that, when the cancellation arrives. However, the guest will pay the airbnb charges.
Now, that it is done, you need to contact airbnb and if the conversation is on the message thread, they should remove the penalties.
If you search "contact airbnb" in the community center search box, you'll find a guide made by fellow hosts, how to contact them from your country.
Good luck