Unable to unlink a Bigin account from Zoho Campaign

Unable to unlink a Bigin account from Zoho Campaign

I have an old Bigin account that not longer exists but somehow it's still linked by my Zoho campaigns. I am trying to unlink the old Bigin account so I can add my new Bigin account, but when I deny access to the old one, nothing happens (it won't unlink the old one). Has anyone experienced this before?