Audible — unauthorized credit card charges

I was charged 12, 43 euros on the 18th of March by Audible. I did not order anything nor subscribe to any services.in fact, I have never even visited their website. I would like to know whether this is a one-time purchase or a monthly subscription to a service, since I'm not familiar with the website. I refuse to pay any bills to a service I have not ordered. I have received a Visa bill (which I'm not going to pay obviously), but what am I to do about it? Please respond quickly.
Anna Eskelinen
[protected]@gmail.com