Custom domain names in Entra still can't verify

We have 3 dns servers that we host on prem in our datacenter. 2 of them have had the same IP address for years, one has changed almost a year ago. So they have been running quite some time doing their job without issue. They are Ubuntu 24.04 running BIND 9. We have a custom domain name in Entra that won't verify. We’ll call it contoso.com. On the same DNS server, I have another zone called tailspintoys.com. We own both domain names. Because I was having issues with contoso,com, I decided to try and add this also as a custom domain name, and tailspintoys adds right away verified. Nnlookup confirms txt and mx records are present. That eliminates any DNS or network /firewall issues for troubleshooting. After further investigation it appears that contoso.com is already claimed by something else that we have no idea what it is, probably something set up long ago and forgotten about and have no access to. Either way, we own both of those domain names and can create txt/mx records or whatever else needs to be done. Whatever is running contoso.com needs to be attached to the one we have so we can either log on the tenant and remove that custom domain name or take it over if it was a resource we had set up and forgot about a while back. We need to get this done as we have O365 licenses to assign to users and an Exchange Online migration to shut down our on prem exchange. We also need to properly get our tenant in our Azure Devops. We are not going to ask our office users to sign in with something else that is not their email address. Thanks!