Perhaps you could try accessing your account via this page.
https://www.telstra.com.au/support/category/email/set-up/how-to-use-webmail
I gave up long ago with webmail and went to gmail.
I have kept my webmail operating but have set it so to it forwards all mail to my gmail account.
I'm hoping that when the new Telstra mail is operating fully things will be better.
cheers