Why does my iPhone say I have used far more storage than I actually have?

I have an iPhone 5C 16 GB. It says I have used 12.5GB and have 0 bytes left. I get that the other 3.5GB is for the software and things within the phone, whatever. My problem is that I have added up all the apps that I have. My biggest two are photos (1.5GB) and WhatsApp (1.6GB) and the rest are tiny apps, the highest being 288MB. I've added it all up and it should come to a total of around 4.5GB. So why does it say I've used the full storage when I really clearly haven't? And how do I change this as it's very annoying? I've turned my phone off and on (the classic trick) and it's done nothing. Any help would really be appreciated. Ideally I wouldn t wanna restore my phone but if that is what you think the best advice is then do say so.

It tells you in the settings what takes up space. Clear your browser cache as maybe you have alot

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