Apple iPhone 6, problem with adaptive video

i have an Apple iPhone 6. I also have a 4gb data plan with EE. I was connected to my home wifi and watched a video via my sky go app. The data should have been taken from my data allowance from my home broadband. I checked my EE app and found 2gb of data had been used in two days which I don't believe is at all possible. EE have informed me that around 1.8gb of my phone data allowance was used by Apple adaptive video. Is there issues regarding this software and whey when connected to my home wifi have I had this allowance, any ideas would be greatly appreciate.

cheers

Russ