I had an existing optus sport account subscibed through google play. Now I got optus mobile plan that included optus sport. Both accounts use the same email.
How do I make sure I get optus sport but don't get charged the subscription fee that I used to have?
If you want to use the same email address as your Optus Sport login, I'd go with Peter's advice.
An Optus Sport subscription requires a unique email address. Your email address shouldn't be registered for both a paid and free subscription.
How to cancel an Optus Sport subscription in the Google Play store
Keep in mind: your subscription will remain active until the initial subscription end date. For example, if you've subscribed on the 7th of the month and you cancelled your subscription on the 1st of the month, your Optus Sport subscription will remain active until the 7th.