Question: How do I deactivate "pending activation" users?
The assumption is that this user never logged into the tenant. A user in "pending activation" status will not have access to the Zuora application unless they have been activated. Now you want to deactivate them to ensure they can never activate the userid - thus preventing them from obtaining access.
To accomplish this, you would need to change the email address of the pending activation user. You can do this by going into Settings-> Administrator Settings-> Manage Users, and select the user in question. Change the email address to yourself and click the activation link. Next, resend the activation email. Once the user is active, you can then deactivate them.