Hi Stepen,
If you cancel your subscription before your 1-year contract expires, you will have to pay 50% of the remaining months and the subscription will cancel which means you will not be able to use it.
If you wish to use it until the end of your contract which ends on 11 September 2018, you will have to pay for all the months and then get it cancelled before it renews for another year.
You may also Contact Customer Care for more information.
Feel free to update the thread for more questions.
Thanks
Kanika