Discovered this on the Optus site when i was paying my bills. Basically free Optus sports subscriptions until 31/07/2017 if you subscribe before 15/01/17.
Check to see if you are elibilge using the link above. Amount should show $0 if you are eligible.
Make sure to cancel before 31/07/2017 to avoid any fees.
Info from website
Catch the rest of the 2016/17 Premier League season and summer of Cricket on us if you subscribe to Optus Sport on selected mobile plans before 15/1/17.
Available to new Optus Sport subscribers only. From 31/07/17 optional Optus Sport is $15/mth. Cancel Optus Sport subscription anytime without charge.
its because they basically bought the rights to the EPL locked everyone out and forced them to become Optus customers and everyone just refused and looked for online alternatives instead
now letting a load of free users join they can say "well look at our great subscriber growth in this period" figuring that enough people will forget to cancel so they will get money out of it