Try going back to http://appleid.apple.com and changing the ID back to the original address. If you can get this accepted, then go to the iCloud preferences/settings pane, stop 'Find My ....', and then sign out. Do the same on any other devices or computers.
Then go back to http://appleid.apple.com and change the ID to the new one. Sign in with that on all your devices.
However if the address which forms the original ID is now not working it can't be validated and it's possible that you won't be able to revert to it. In this situation only Support can help you.
To contact iCloud Support: if you currently happen to have AppleCare, either because you recently bought Apple hardware or have paid to extend the initial period, you can contact them here:
http://www.apple.com/support/icloud/contact/
You will need the serial number of the covered hardware.
If you are not covered by AppleCare, then - in common with other free email services - there is no free support and you may be asked to pay a fee.