Hi We went to verify our domain but when we tried, we received a message from Facebook that said our domain had been verified by someone else. We suspect one of our ad companies may have set up the domain in their account rather than ours.
How would I be able to learn who outside of our company verified our domain so that we can solve the problem?
You'll probably need to reach out to your ad companies to see if they have your domain in one of their Business Managers.
You can also try reaching out to Business Support: https://www.facebook.com/business/help/support. However, if the BM that has your domain is active, Facebook legally cannot give you information about who owns it. If the BM is inactive, they can release the domain.