You need to cancel monthly subscription by yourself.
The following steps will allow you to cancel your Tab Pro subscription on your Android device:
- Open Google Play.
- Open "My apps" section.
- Switch to "Subscriptions" tab.
- Tap on the Tab Pro app subscription.
- Tap on the "cancel" button for subscription you want to cancel.
Don't worry your Lifetime will be in good standing after you cancel the monthly subscription.