Lost my last work-mail access wich is linked to the account. So I can´t close the account, that I'm paying with my credit card.
If you're unable to sign in to the account, you would need to contact Support directly. Visit the Support page while you're NOT signed in to a Dropbox account, including these forums, and you'll see an option for Billing issues. It's best to use an Incognito or Private browsing session to make sure you're not signed in.