Data being chewed up on android when streaming

[JFlamestar]

So Spotify has eaten up a huge chunk of music, both times from a few hours of streaming music (as evidenced in the screenshot).
Music streaming quality is set to normal, downloads are set to WiFi only and the estimations are that 1gb of data = 24hrs.
So why have a few hours of browsing music on two different days totalled nearly 3gb of data?!