try to restart, see on android with es file explorer or the file still exist, find the trash folder and delete that one. It is maybe hidden but its named like .trash 1000 i believe but its an trash folder i can't say much more since i dont have an phone anymore for 2 months now. Or you must find some app to find big and large files or some trash remover app.
I also had the same problem as you had on my s2 i had my wth moment when that happend and i needed to remove an folder named something with trash and i had my storage back
i hope it also works for you.