Cancel from inside the Duolingo app (Duolingo's documented in-app path)
- 1
Open the Duolingo app
- 2
Tap the Super icon at the top of the home screen
- 3
Tap Settings (gear icon)
- 4
Tap "Manage subscription"
- 5
Select "Cancel subscription" and proceed to cancel
- 6
Confirm cancellation through Google Play Store or App Store or Alipay
Source: duolingo.com — the provider's own documentation for these steps.