Why I can't change the notification sound for messaging app?

[Stefan Neata]

Hi! Today I wanted to change my notification sound for all apps on a LG G2 mini(android lolipop 5.0.2) using this path: settings>sound>notifocation sounds. Well it worked to whatsapp and other apps but not for messaging app... well it changed ... to a BEEP or a piano note(how do you wanna call it). I restarted the phone >nothing. I changed the notification sound from messaging settings (messages>options>settings>notifications settings>notification sounds) and... nothing. I deleted the application data and forced stopped the messaging app and still nothing.
What shoud I do to fix this announg thing?
Thanks.