How to completely clear Instagram from iPhone?

I'm having an issue where I'm not able to promote posts on the Instagram app. I was told by Facebook support to delete the app but when I reinstall Instagram after deleting it, all my data and account info is restored. It's repopulating the same accounts that I had signed in from that device earlier, so I assumed that it may be some local data. It should ask for a fresh sign-in. How do I completely delete the Instagram app and all documents & data associated with it from my iPhone?