I have a SAMSUNG phone. Of my 125 GB SD Card, I have used 4 GB. This is also correctly shown in the Settings-Storage.
However, when I now try to save anything to the card, I get the message "Not enough space on the SD Card", or with smaller files "Your SD card is almost full. You may not be able to store photos....". This drives me crazy. I backed-up the SD, reformatted it and wiped it with MiniTool partition wizzard. I also checked that there are no dead segments on the SD Card, a 6 hours process - all green. I have no idea anymore.... :-((