Device memory full for strange reason?

My device memory is saying 'storage full...' etc etc, so I deleted the largest apps which I assumed were taking up the space. But no difference has been made. I also moved very large apps to my memory card but no difference. I can't even download the smallest app without the phone saying 'error, insufficient memory' or re-install the apps I deleted to make more space.

I have a samsung s4 mini

PLEASE HELP ME! PLEASE HELP ME!