1eStar: The app should still be in beta. I have a monthly combo recurring. Decided to add the $8 weekly data addon through the app. It worked sweet. Except; there was no notification, and there is no way through the app to stop it recurring. I had to use the mobile website to stop it recurring.
On your Dashboard, if you select Add-Ons at the top of the page it will show you your currently active Add-Ons. Select the orange > next to an active Add-On and it will display the details of the Add-On and give you an option to deactivate it.