If you are having trouble removing a domain using the Office 365 management portal you can use the Microsoft Online Services Module for Windows PowerShell to help.
First off download the module and find out a little bit more about the MSOL module from here, http://onlinehelp.microsoft.com/en-us/office365-enterprises/hh124998.aspx.
Use the following cmdlets to connect, identify and remove domains.
the following command will list the domains you have added to O365.
Change the default domain.
Set-MsolDomain -IsDefault -Name exchangegeek.onmicrosoft.com
Remove the domain.
Remove-MsolDomain -domainname exchangegeek.com –force
Hope this helps, it worked for me out moving domains between tenant organisations and not getting any response to my “service requests”.