This didn't turn out the way you wanted it to.
My recommendation (for others reading this) is this:
Don't try to "close" the client aspect of your Upwork account.
Just don't use it.
If I don't use the client side of my Upwork account, then it doesn't cost me anything and doesn't hurt me in any way.
I get this error message "Oops! Username is incorrect when I try to Sing In. Looks like my account was deleted. Can you please help me to restore it and grant the access to it?
I have an account with Upwork that I no longer have access to that email. I'm setting up a new profile and the system is saying my phone number is already associated with another account; how do I fix this?
Please be reminded that Upwork does not allow users to have multiple accounts. Could you please click on my name and send me a PM with more information about your second account, including a username and email address of it? I'll check that for you and assist you accordingly.