Google Play says it explicitly

Google’s help page says uninstalling an app does not cancel its subscription. Cancel from the subscriptions area using the purchasing account. Stopping renewal on a committed payment plan also does not erase remaining scheduled payments.

Sources[1] Google

Check the Apple receipt

Apple directs users to Settings, their name, then Subscriptions. If a subscription is missing, inspect the receipt and billing provider. Its trial guidance says to cancel at least 24 hours before the trial ends if you do not want renewal.

Sources[2] Apple

Keep the confirmation

Save the cancellation confirmation and the displayed end date. If a charge has already occurred, follow the billing provider’s refund process separately rather than assuming that cancellation returns past payments.