If your account is a part of a “billing group” this allows you to share a subscription and save money by making one payment to cover the combined total employees in a number of linked accounts.
If you see an alert that you are over your paid Employee level it may be that your account is linked with other accounts and that combined total is higher than the paid level. You can see at the top of your manager homepage if you are a part of a billing group.
If Employees cannot be deleted or unnecessary accounts unlinked to get your maximum below the paid level, then someone from your organization (from any linked account) will need to go to the Settings>Upgrade page and choose an upgrade option.