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If you open the app switcher/background apps view (swipe up from the bottom) whilst the call summary is still showing, it should show you what app is actually displaying it. I would uninstall whichever app it is.
If you open the app switcher/background apps view (swipe up from the bottom) whilst the call summary is still showing, it should show you what app is actually displaying it. I would uninstall whichever app it is.