Just like Cancelled Subscriptions, a canceled trial means the same: a user opt-out from prolonging subscription. That means you won't get a first payment (any other until a user restores a subscription).
When a user in an auto-renew off trial state you still have a chance for Restoring Subscription. Try Adapty's win-back campaigns: as soon as a user Cancels a Trial, send promotional push notifications with a sweet discount. At least, you can get something.
Apple/Google will let you know about Refunds via server2server notifications. Handle, store and process them to build custom views with Cancelled Trials analytics.
Adapty does everything for you automatically. Simple install SDK for your platform, open Advanced Dashboard and you're ready to go!