As we noted when the API changes first took effect in 2015:
Apps don’t have to delete data they’ve already pulled. If someone gave your data to an app, it could go on using it. However, if you request that a developer delete your data, it has to. However, how you submit those requests could be through a form, via email, or in other ways that vary app to app. You can also always go to your App Privacy Settings and remove permissions for an app to pull more data about you in the future.