@Christiane295 I hope you can understand English. I can understand your German but it is easier for me in English. If you did not get a confirmed notice than you did not book a reservation. This is just a place where host give support to others, hosts and guests sometimes. If you can find the telephone number for the Airbnb in your country call them - or call the host.
On your Profile/where your picture is you find travel or switch to hosting. That is where trips booked will appear. So keep in touch with Airbnb and say please cancel just in case.
Good luck, wish I could help you more - best regards, Clara