Hey there! Thanks for reaching out! If you have access to the old account, you’ll want to make sure you also remove the domain from the “Domains” tab if you haven’t! This can be found in the left column of the UI, then you’ll click the domain name, scroll allllll the way to the bottom and select “Delete DNS zone”.
If you still can’t add it, we can remove it for you once you create the DNS TXT record mentioned on this guide: