Unable to delete Storage on phone

[daaki93]

I have Spotify Premium, so I started downloading songs to listen to them offline. Now, after  an update all my songs aren't downloaded anymore. The little green arrow next to the songs disappeared. But the files didn't.

I thought that maybe if I redownload them, they will be recognized or deleted... but NO. They were only added on top...

Even emptying the cache and uninstalling and reinstalling the app, trying to delete them with a File Manager, nothing works, I can't get rid of 13,5 GB of Data.

I can't even use them. They are just sitting there.

How do I get rid of the files?