How do you cancel duolingo plus?
I was unaware there was a Duolingo Plus, perhaps it depends on what device you're using. Maybe you can check the settings?
Edit: Apparently it's for Android users, though I'm unfamiliar with Duolingo Plus. I'm not sure if you can unsubscribe or uninstall the app. You should probably talk to a moderator about it.
Maybe via the App store on your device?
Android help for "Cancel or change a subscription on Google Play" https://support.google.com/googleplay/answer/7018481?co=GENIE.Platform%3DAndroidhl=en
IOS help for "View, change, or cancel your subscriptions" https://support.apple.com/en-us/HT202039