SAMSUNG GALAXY M30S DOES NOT RETAIN DATA ON THE SDCARD!

SAMSUNG GALAXY M30S DOES NOT RETAIN DATA ON THE SDCARD!

Hi All
I really need some help with this one - I have a M30S which is only a couple of years old and I have a problem with data - Mainly MUSIC - MP3 and also MUSIC VIDEOS -. Mp4's etc.

So, I downloaded the music and videos etc and then - Using File Manager Plus App (From Google PS) - I Move the files to the SDCARD.
2 THINGS - A) The Files I moved are simply not in the Folders I pasted them in to! The Newly created folders are still there - Just no files in them!

B) Less annoying but still not right - All files which are in the Downloads folder are still there - Whether I have MOVED, (or COPIED THEM). Also if I accidentally refresh the folder by scrolling down or up the screen ALL the files reappear - Including ones I have deleted earlier!

I have tried several different New SDCARDs and read information on the Samsung galaxy M30s on Samsung's site but none of it has been any help! I have tested the SDCARDs - Using "True SD CARD CAPACITY". The result shows that an SDCARD with a total storage of 512GB only has an available Capacity of 3GB - When there is no data over 1GB Max! Actually on the card!

Any ideas with be welcome!

Thanks for your help

J