C4 internal storage 16GB?

[Zhnovia]

I bought this Xperia (C4, or at  the store E3) because it has 16 GB internal storage. But I send to you my screen shots of my phone' s settings..... 

 Thanks! 

[Zhnovia]

Settings -> Storage. That confuses me that the phone tells that the internal storage is 16 GB, but you explained that to me. Is very helpful!

This is inside the internal storage, from Settings

[Zhnovia]

When the 'diagnostic control' is red the internal storage from the Settings isn't red, but the phone doesn't work properly. Now at 13,08 GB internal storage from Settings is the limit to have my phone work properly.