So-called "free users" should have ALL their rights checkboxes unchecked, 100%, including the right for the Free Use section.
A paid user (full user, normal user) is someone who has access to the system, a user who has credentials to view, create, or update something. It's someone who can log in, in normal mode or internet-kiosk mode.
A free user (team member) is essentially not a user of the system, but just a named person in the system, for whom you can keep records of. A free user does not have access. This is beneficial for example when someone leaves your company, then you can convert the paid user to a free user instead of deleting him/her, to keep records of that person's actions.
Please do not worry, the billing system does not take money automatically for additional services like:
Upgrading pricing plans.
Purchasing Skype training hours.
You can ask us to delete this incorrect invoice by opening a support ticket, or you can wait till 14 days has passed, after which it will expire automatically.
In any case, such proforma-invoice doesn't impose any obligations on you.