Equalizers are not working I have been using Equalizer+ and a while back it stopped working. 

I was told that it might be interference with other apps, so I deleted/disabled all other music apps (except default music player) and it didn't work well.

I referred to Android 5.0 (Lollipop) music equalizer? and I could not find MusicFX anywhere in my apps.

It doesn't work with Equlizer+, Bass Booster EQ, Shuttle, Rocket Music Player and any others wither.

I have ran out of options and I really want sound quality back. My phone is LG Leon and it is running Android Lollipop (v 5.1.1).
Yep! 
A known issue :( 
Some platforms such as Samsung Galaxy Note 5 (mine has official firmware/lollipop 5.1.1) comes with a built-in equalizer which is disabled by default,
I've searched for ways to permanently disable it and use an external one ("bass buster pro") and I did, but apparently there is no way to do it, even after completely disabling the built-in services (to prevent resources from being "locked" by the internal equalizer), 
Apparently it is not the issue, 
perhaps in more "open" firmwares or different devices it can work, from reports around the web Android 6 (marshmallow) will enable a workaround, 
Or, maybe - for rooted users, a XPosed module can patch it in memory, 
(but due to many bugs and bootlocks happening when installing XPosed on Android 5.1.x+, mudule developing might take a while). 

Not 100% bad news though, You can install VLC player (or even a legacy winamp apk) which has a built-in equalizer, which, although limits the experience to a specific application, provides a working solution for bass enhancements for your selected playlist (as long you are playing it through the app. that is... )