As per the instructions in the KB article:
Create and manage cases
If you are the owner of a Tableau product key, you can use the Tableau Customer Portal
to create and track cases with our Customer Service team (for billing and invoices)
or our Technical Support team (for help with using Tableau products).
If I don't have an account, how do I create an account ?
Just use the create an account option at the login page ?
If you don't have an account yet --
and it means you've not been buying
anything from Tableau -- then simply
creating an account doesn't help either.
If your company is a customer of Tableau,
you can ask the person in your company
who has a Customer Portal Administrator role
to add you to a Customer Portal:
Besides, you've got the Tableau ID already --
the one you're using right now on the Forums.