High data usage while OFFLINE mode

[b0bbYboy]

I recently bought an iPhone 6 128GB just to have ALL my playlists in spotify, about 2000 songs in total, in offline mode so I dont use colossal amount of data from my service provider. Well, even though I have played nothing but offline mode playlists, somehow I have used shy under 5GB of data in the last 2 weeks. 

I have used offline mode in the past, when I had a 64GB iPhone 4S, with no issues but this time it seems like its not even using my downloaded songs from playlists and streaming them right off LTE. 

I would appreciate it if anyone forwards this to the developers or helps me out figure out what Im doing wrong.