Can't Verify Domain Ownership

Good afternoon, 

I am attempting to verify ownership of my domain, www.iea-corp.com, and have received the following error: 

	Sorry, we couldn't add the domain iea-corp.com is a subdomain of a domain that was already added and verified by another customer, so you can't add it to your account. If you are not sure how to do this, ask a question in the Office 365 community. Include this error message so others can help with the issue.

My site and e-mail are hosted by a third party, and we would like to maintain our existing hosting setup for these assets.  Could you please assist us in verifying ownership of this domain?