You should also be able to arrange an extension via LIVECHAT online (Phone access does appear overly time consuming).
The Optus page states: Important: If you've received a notification about a system upgrade, or if your account number is 11 digits long and starts with 62, the information on this page may not apply.
Seems 61 has been added to the list?
Perhaps contact Optus and ask why your account number begins with a 61 and if you can change it? Has it changed lately as far as you know?