Can't change email address

I have tried changing my email address. I even clicked on the verification email - but then it logs me in with a new account under that email.
Also it prompts for the verification password - which even if copied and pasted i.e. exactly the password - it fails.
Cf. Changing Email Address Login Error
The admin email is contact@online-go.com

continued here:

https://forums.online-go.com/t/re-how-can-i-associate-with-a-different-google-account/48699/18