If you want to find your unfollowers on Twitter, you could use your own self-hosted script instead of relying on a third-party service.
There are several advantages: no ads, no tracking of your IP address / geolocation and activity, no risk of relying on a third-party service that will become unavailable in the future.
If you are using a “protected” Twitter account where all your tweets and following / followers are private, it may also be a good idea for privacy to avoid using a third-party service that could see all your followers.
By using your own script, you will own the source code and it will always work unless there is a major change in the Twitter API.
The script could be used manually in your web browser everytime you want to see who unfollowed you or automatically everyday by sending you a notification by email or private message (a.k.a. direct message) on Twitter with the name of the accounts that unfollowed you (for the automated solution, you will need to have a server configured).
If you are interested by a Premium script to find who is unfollowing you on Twitter, you can contact me here.
You may also be interested: Facebook unfriend detector script