[Moseby]

Okay,

So the phone is not mine. It's my sisters, she just got it from a friend. The friend had factory reseted it so it was completely as "new".
Anyways!


The phone is totatlly locked, can't call anyone or anything because the phone is fucked up.

When typing this, the Cache memory is over 100GB (YES GB)

When deleting cache, I have to restart the phone. Now the cache is on Spotify (going up and up over 100GB again)

It's going from Google Play Services > Spotify and back all the time when trying to delete.


What the fuck is wrong?

[6LACK EA6]

Although your error is quite odd for such a ex-flagship device it probably happened when the phone was 'factory resetted' it's cache should've also been cleared just to be on the safe side, since your device didn't have it's cache cleared such errors tend to happen.
As far as solutions go, you should initially try clearing your cache through recovery mode, follow the steps below:

Spoiler (Click to View)
1. Turn off your Galaxy S5.
2. Press and hold the Power, Volume Up and Home buttons simultaneously.
3. You can release them when you see the Samsung logo with Recovery booting written in blue at the very top of the screen.
4. You will be brought to the Android System Recovery screen (or a custom recovery if you have one installed – if so, your steps will be slightly different, but basically the same as described here).
5. Use the volume buttons to scroll down the list to highlight Wipe Cache Partition and use the Power button to confirm your selection.
7. You'll see a notification at the bottom of the screen in yellow to show that the system cache has been wiped.
8. If Reboot System Now is not already highlighted, use the volume keys to highlight Reboot System Now and press the Power button to confirm.
9. Your Galaxy S5 will reboot with a fresh system cache.


If this doesn't work I'd suggest flashing a stock firmware or a custom ROM which would fix the issue. Flashing a custom ROM requires Root, which means you'll loose warranty of your device.