Try GetDataBack (FAT or NTFS version, depending on your USB stick)
Unfortunately that program is not free, but it does work (and it says also "Get everything back even when the drive's partition table, boot record, Master File Table or root directory is lost or corrupt. ")
Just download it off somewhere, or use the Trial just to make sure it'll do the job (then you can "buy" it
)
Oh, you already tried this. Ok, well.....I'd say format, but wait for somebody else who knows what they are talking about 
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