Help System data now 20gb after upgrade:(

[Mrfunks]

hi upgraded my phone to lollipop and it as assumed I have lost all media from previous install, which I wanted. Unfortunately it has created 20gb of unusable space in system data.

I'm assuming that the previous kit kat music and pictures haven't been correctly deleted, as my phone size now thinks it's 10gb with 8gb free, although when you click on storage it shows its 32gb.. With 20gb of system data.

I have tried several factory resets, rooted phone and deleted dalvik cache etc, via root manager. How can I resolve this.. As 8gb will not last me long. Where is this 20gb Amy help would be much appreciated.

Thanks