Its illegal for Optus to send you marketting SMSs without explicit consent. If they do they must provide an option to stop you contacting them. Similarly for emails their will always be an unsubscribe option at the bottom of the email.
Of course Optus may still send bills or other legal info (lije changes to terms and conditions) but they should stop bugging you.
As a matter of course you should also register your mobile and home phone on the national DO NOT CALL register. Its government run and all Australian businesses must not contact you for marketting purposes once registered (lasts 10 years)