The operating system has nothing to do with it. Streaming video or using Facebook or similar apps are the likely culprits. Facebook continues to suck data in the background as it monitors where you go even after you have left their website.
40 minutes of video at low res (480) will take 250-300MB of data. At 720 resolution (as with Amazon content) that goes up to 1GB in an hour.
The ISP's know that this is occurring and that is why they sell people on 4G and have stopped rolling out DSL or anything else that would compete with their premium priced 4G service.
We fixed the problem by going to a T-1 land line that is half the speed of 4G but still fast enough for 720p content and where we have no monthly cap. The 4G was costing us $180 a month and the T-1 circuit costs us $252 a month.