Well, we can't see the card.
And we don't know if my_music is the folder they should be in.
And we don't know exactly what it "says".
And we can't see if you put them in there.
In fact, we don't even know what phone you have, because you still didn't tell it.
We even have to believe you "changed" the transferred files to mp3 format in the right way and gave them a valid name with the right extension. You didn't tell.
So all we can say is, that something is wrong.