Hello Casper,
Please go to the downloads section in your account here: https://www.wcvendors.com/my-account/downloads/
You should have a delete button there- as well as your license key(s).
Since a lot of users seem to have difficulty deactivating the license, I have already gone and deactivated this on our end- you can now go to: wp admin > settings > wc vendors license and try to activate it again on your website.
In the future, if you need to deactivate the license, go to wp admin > settings > wc vendors license, an, you should have a check box that says Deactivate. Check that and hit save.. If that fails- let me know and I can deactivate it for you.
Also you used this email: pie@parbl.eu when purchasing Pro- so that’s the email you will need to use when re-activating the license.