Airbnb Fradulent and unauthorised credit card transaction

Airbnb processed an unauthorised charge on my old credit card (which I haven't used on their platform in 12 months). When I queried it, Airbnb asked me not to report it as a ********** transaction and that they will refund me. However, I did not get a full refund in local currency, and when I queried it, Airbnb's response is that there was a currency fee and they will not refund me the difference and do not wish to engage further on the matter.

It is horrific for me to learn that 1. They keeping my credit card details and can charge it when they want to without any authorisation from me (is this even GDPR compliant?), and 2. This is how Airbnb deals with ********** card transactions.

I encourage everyone to check and remove your card details from Airbnb asap!