Are you logging faults when it happens?
If you are, then call Optus on 133 937 and speak to billing, they'll be able to see the notes of where you've called up for faults and can discuss compensation. Please note, you are on a consumer grade service so there is no promise of refunds or credits, as its a "best effort" service.
1) you'll have needed to raise a fault with us. You'll need to have a fault ticket, which states that outage start date
2) Contact us and we'll provide you with a pro rata credit for the number of days you've been without service.
Also note, if the outage wasn't resolved in the timeframe set by the customer service guarantee, you might be eligible for additional compensation.
For more info, head to ACMA website.