"ive fully formated it "
Unfortunately at that point it’s not a SanDisk problem, it’s yours. What was manufactured, block size, cluster alignment, etc are gone.
Next time you want to delete files/folders on a USB drive use Windows Explorer to remove them, and delete them from the Recycle Bin should they end up there. Or you could simply write your files along side the SanDisk files. Formating worked with old simple USB drives years ago but this modern stuff needs a more caution approach. IMO
