App subscriptions are managed by the store you bought them from — not in the app or by email.
- Open Settings → tap your name at the top.
- Tap Subscriptions.
- Select WhoIsThis → tap Cancel Subscription and confirm. (You may need to scroll down. If there's no cancel button, or you see a red expiry note, it's already cancelled.)
You keep access until the end of the current billing period. Official Apple page: https://apps.apple.com/account/subscriptions · more detail: https://support.apple.com/en-us/118428