If you subscribed to Numeo through the Apple App Store, Apple handles the cancellation, so it has to be done in your Apple account.
1. On your iPhone, open Settings.
2. Tap your name at the top.
3. Tap Subscriptions.
4. Tap Numeo.
5. Tap Cancel Subscription.
You'll keep access until the end of the period you already paid for.
Full steps from Apple: https://support.apple.com/en-us/118428
If you can't find Numeo in your Apple subscriptions, contact our support with the email or phone number on your Numeo account and we'll check it on our side.