Most app subscriptions are billed by the app store, not the developer. That means deleting the app cancels nothing, and the charge continues until you cancel in the store's subscription list.
Free trials convert automatically, usually a day before the stated end date, and reminder emails are not guaranteed. A trial started on a family member's account complicates it further.
Prices also change at renewal. Stores must notify you, but the message arrives as an easily missed notification rather than a blocking prompt.
Refunds are possible but time-limited, and they go through the store's own request process rather than the app's support desk.