Why does Android 6.0 ignore my decisions?

[AC Question]

I've recently changed my mobile to one with Android 6.0 and I struggle with ringtones. Mobile totally ignores what I pick.
There's an app called Play Music (which is default) and lets me to pick any mp3 file (from an SD card that works well - checked on another mobile and laptop) as a ringtone. The problem is that when I set it to alarm clock or to a single contact - it plays whatever random default ringtone it wants, while when I check settings the one I marked is set.
I've tried using ES File Explorer File Manager, but the problem didn't disappear. So it's that I follow all the steps there are, press the tick button(or okay button), I check settings and it's marked as I wanted, but when the phone rings, the ringtone is different. So I get back to settings, the chosen ringtone is named "Unknown", I click it and see the ringtone I've picked marked as the one who rung. And I'm like - wth
Can someone please help me? I could stand not being able to change it, but it's not what I've expected when I bought a new phone

My phone: myPhone Prime Plus v.1.4.
Android: 6.0
Also - my mother has same phone and there's no such problem, she doesn't have Play Music, but another music app(that was default)

 

[mhinc]

I've recently changed my mobile to one with Android 6.0 and I struggle with ringtones. Mobile totally ignores what I pick.
There's an app called Play Music (which is default) and lets me to pick any mp3 file (from an SD card that works well - checked on another mobile and laptop) as a ringtone. The problem is that when I set it to alarm clock or to a single contact - it plays whatever random default ringtone it wants, while when I check settings the one I marked is set.
I've tried using ES File Explorer File Manager, but the problem didn't disappear. So it's that I follow all the steps there are, press the tick button(or okay button), I check settings and it's marked as I wanted, but when the phone rings, the ringtone is different. So I get back to settings, the chosen ringtone is named "Unknown", I click it and see the ringtone I've picked marked as the one who rung. And I'm like - wth
Can someone please help me? I could stand not being able to change it, but it's not what I've expected when I bought a new phone

My phone: myPhone Prime Plus v.1.4.
Android: 6.0
Also - my mother has same phone and there's no such problem, she doesn't have Play Music, but another music app(that was default)

I don't use any 3rd party apps to use custom ring tones. Just stick the ones you want to use an a folder called NOTIFICATIONS and boom pick the one you put in there from the list