Unable to delete old calendars from Microsoft Outlook Android App
I found this discussion helpful: 

http://answers.microsoft.com/en-us/outlook_com/forum/osettings-ocalset/deleted-calendar-showing-up-in-ios-outlook-app/2812d42a-4bdd-464c-9077-b1517d6f665c

What worked in my case was: 

1.deleting both outlook account from account settings AND outlook app


creating microsoft exchange account according to instructions from the link above
installing once again outlook app, but this time using not outlook settings but Microsoft Exchange settings