Error trying to change Apple Id
I'm using Safari 9.1 on a Macbook to try to change my Apple ID email address, following the instructions in Change your Apple ID - Apple Support
I get as far as entering the 6 digit code from the verification email sent to my new email address, but when I click Verify a little yellow box pops up above the code saying "Your request could not be completed because of an error.". I've tried resending the verification email and using the new code multiple times. I've also tried using Safari on an iPad. Same error every time. I can't find any reports of this error using Google. The Apple Id account is working fine but still with the old email address when I sign in my devices again.
Any ideas?