One of my customers contacted me after BT informed them that they had nearly used up their 50GB monthly allowance. They only use their computer for occasional light surfing and emails so it was a surprise to them that they had used so much data.
The problem turned out to be a Windows 10 update downloading, installing, failing then downloading again repeatedly. At just over 700Mb this quickly used up their monthly data allowance. Many people have also experienced this problem and posted their frustration online.
There does not currently appear to be a solution for this – even performing a clean install of windows does not help! If you have this problem too and have a capped data allowance I suggest that you disable your windows updates until the next big Windows update is release sometime in April.
Read more about it here