The Tenant's data is not completely deleted when you click De-Activate.

The Data is archived in the system and can be restored.

In order to completely delete this Tenant's data -
First De-activate the Tenant on this page "All Tenants",
-Then click "Settings" in the top right corner of this page,
-Then on the settings page click "Frozen Tenants",
-Then click "Completely Delete"

After this process the Tenant's data will be completely removed from the system