I'd recommend checking out Crowdire (https://www.crowdfireapp.com/).
You can sign in using Twitter immediately, and sort users you follow by those not following you back, those who have unfollowed you, those who haven't been online for a specified duration of time etc. You can unfollow people directly from the site through these lists.
Some features, taken from their website:
- Finding inactive users and your unfollowers - unfollow them if you wish to
- Finding relevant users to follow using our insightful “Copy Followers” feature
- Keeping track of how your social media updates affect your follower/unfollower stats
- Checking the relationship between any two Twitter/Instagram accounts and doing a whole lot more.