I can't find files taking up space in my android phone
I also had the same problem with my Android.

But after doing some researches i found that the google apps Google docs Google sheets and Google slide are taking much space .

When i looked for the app info of these apps, i found that all of these are taking at least 200mb of space where as i never use them.

So i cleared the data and all problems solved.

But if still the problem does not solve, you should finally factory reset your device.

Hope it helps.