Salut @Angèle24 ,
Yes !
it seems that very frequently CS makes a decision without talking with both parties, and without notifying the host.
We've similar exprerience like your case recently.
Once, the CM has make his decision, that is no more responding and refuse for futher discussion and inversitigration.
As @Helen3 suggestion, do consideration try calling back to appeal to a new rep, contacting Airbnb on Twitter or Facebook.
Yet, we just dropped the case. Learn the lesson and moving on.