All subscriptions on iOS are managed via your iPhone's App Store settings.
To cancel the automatic renewal of your subscription, simply go into your iPhone' settings and select: Your name at the top of the screen -> iTunes & App Store -> Apple ID -> View Apple ID -> Subscriptions, then tap on your subscription and cancel automatic renewal.
You can get more information here: https://support.apple.com/en-us/HT202039
Do not hesitate to contact us at firstname.lastname@example.org to give us feedback and share what we could have done to keep you as a subscriber!
- Left Menu -> then "My Subscriptions".
- Then tap on your subscription and cancel the automatic renewal