Cannot access my account but can get into webmail
That's your Optus.com.au/myaccount that you're talking about?
Webmail and My Account aren't related services. What sort of issue are you having on your end?
It's not recognising your username and password, or you're unable to view your linked services? I've linked an article below, that might be helpful. Let us know, happy to help out.
My Account Troubleshooting.