Did you log out?
Just deleting the app does nothing as far as Facebook is concerned.
If you ever logged in with a browser or any other app that has ties to Facebook- like for instance a game that uses Facebook to save your game info or xonnect to your friends- then that could be it as well.
Try getting on Facebook with your browser, and then log out.
Do the same for every single device you have access to- whether you remember ever being on Facebook with that device or not.
Untie any games or other apps from your Facebook account.
Also, there is no way to 'delete' a Facebook account.
You can deactivate it, but it still will exist.