Apartment in Brussels Illegally Rented on Airbnb

I am the owner of an apartment in Brussels. A couple of months ago I discovered that the person who rents my apartment has listed it on Airbnb. First of all, it is against the regulations in the apartment complex. I already had to pay a 500-euro fine. After calling the person who rents my apartment several times, she still refused to remove the listing on Airbnb. I’ve send several mails to the Airbnb website but with no response. I don’t not understand how they can accept this or not respond. Is there a quick and efficient way to contact them or must I take legal action, not only against the person who is renting my apartment but also Airbnb itself? They are making money out of it, and it is illegal because as a owner it is against regulations, and even the law in Brussels.