There has been a fair amount of discussion on this forum about suspending your contract. It seems it can be done for mobile at $5 per month but no definitive answer on broadband. Here is a link to an Optus post which days you need to ring them.
Here's another link to a discussioni held on the forum but might confuse you more:
Hey @Keivn - I've taken a look into this for you and I can confirm that we're unable to temporarily suspend fixed internet and landline services. Apologies for any inconvenience here. If you did need to chat to someone about this in more detail, I'd recommend giving our Customer Care team a call on 133 937 or chatting to them here. They may be able to look into alternative options for you.
Definitive answer to fixed broadband. I'm not going to be able to claim all that money, just have to have a glass of cheap white tonight.
Mobiles - can suspend as Optus owns the network
Nbn/resold Telstra dsl based - nbn/telstra still want the wholesale cost regardless so not available.
Optus hfc - perhaps?