In the Optus My Account portal if you click on My Profile at the top of the page a contract tab appears. Failing that I would jump on the live chat link below and ask support the question.
Here's a tip - you can set expiry dates for your mobile in this website and app - https://www.getreminded.com/
Reminders ensure you have time to negotiate a new contract and not overpay. Plus for energy, car rego, passport + lots more.