SD files go away after copying files to it

[trouble74us]

I am using a win10 machine and an note20 ultra. I am trying to copy mp3s to the phones sd card, from file explorer it says the files are copied but when i go to use them the directory is empty. it use to work a while ago, am going on a trip and want so music to go with me.
I have tried taking the sim card from the phone and doing the copying on my desktop, but it magic window says that the directory's are read only, but when the sim is in the phone it says they are not read only, the folder names stay on the sim just the files are going away every time i copy them.
when i copy file to the sim card the explorer says they are there, i play a file form the sim folder but when i diconnect the phone the file keeps playing, like it is reading from the file from where the file came from on the other hd, it is not reading from the phone i just disconnect .
help
this is the first time i have ever posted for help from someone.
thank you
trouble
aka dennis rimmer

 

[Grizzly]

To make it clear: where do you copy the music files to, the SD card or the SIM card?? these cards are two different things. The SIM card is the one that allows to connect to your providers network and usually cannot be used to store files on it, so I am assuming that you copy the files to the SD card.
However, does the program that you use to play the music, has even access to the SD card?? by default this has to be established first as the standard path for any type of file is not the SD card but the phone memory instead.
Please verify that my assumption is correct...