System has 0 free ips -- IP stuck with addondomain.oldcomain.com - where can I remove

Changed an IP based site to a Namebased site in hopes of re-using the IP address for a new site that needs a cert.

However, the IP that should have been freed up is now showing as used by old-addon-domain.old-domain.com where old-addon-domain was deleted some time back.

How can I free this IP up for reuse? When I click "rebuild IP pool" I get the error that System has 0 free ips.
old-addon-domain.old-domain.com is not in the dns zone for old-domain.com
And there is no old-addon-domain.old-domain.com account to delete from whm.

Any ideas?

 

Figured it out - had to manually login to the old-domain.com's cpanel and delete the cpanel-created subdomains that cpanel automatically created when the add-on domain was added (but that were not deleted when the same add-on domain was deleted from cpanel and that were not changed to the new IP address when old-domain.com was changed from ip based to name based.)

Now WHM is correctly showing the IP as free.