Nokia 5130xpressmusic
Phone memory full

30 mb is the phone memory for 5130... i have used not even 5.4mb of phone memory but when i checked used space and free space it said "3.7mb free of space" used space was gallery 4.4mb, messege 114kb, application 945kb or so, bookmark 3kb and so on, not even 21mb... please guide me what might have happened