This app was mentioned in 3 comments, with an average of 1.00 upvote
Check out Followers Insight, it lists all the accounts you're following but aren't following back and let's you visit their profile quickly so you can unfollow them.
I used it a long time ago and it worked.. have no idea if it'll still work.
https://play.google.com/store/apps/details?id=com.skyfireapps.followersinsightapp&hl=es
I use Followers Insight
This is for android though. I'm not sure if they have an app for apple.
'Follower insight for Instagram' works great for me. You can also add multiple accounts. Here's the link - https://play.google.com/store/apps/details?id=com.skyfireapps.followersinsightapp