Windows 10 blows your monthly usage limit!

[#1]

A word of warning for customers on a monthly usage cap...
My elderly parents have a 10gb monthly usage limit as their usage is never more than 2-3Gb per month, but a couple of weeks ago they started seeing warnings from Plusnet informing them that they were approaching their limit. When I looked at their usage stats I discovered that 5Gb had been downloaded during just two days.
It turns out that Windows downloads the install files for Windows 10 even if you haven't opted to "reserve" it via the "Get Windows 10" app (you may have noticed this appear on your taskbar last month). As the install files had been downloaded, I thought there would be nothing to lose and installed Windows 10. Unfortunately it has since installed another couple of Gb of updates, blowing my parents' monthly limit, which they were charged for.
To make matters worse, I've read today that Windows 10 uses a peer-to-peer network (similar to BitTorrent) for distributing Windows updates, and this will further eat into monthly allowances. It is possible to turn it off though:- http://www.techkhoji.com/stop-windows-10-from-using-your-upload-bandwidth/

[#2]

Hi andyste1,
They'd probably benefit from changing over to an unlimited package.
Don't worry, I'm not going for the "hard sell" here they'd most likely make a saving.
Feel free to send me a PM with their username so I can check and advise you further on that.
Adam

[#3]

I think this is evident above but Windows Updates default to sourcing from your computer for other people.
So the usage on outgoing data is unlimited and dependent upon Microsofts' algorithms .
Many thanks for posting your experience- I had no idea and I am on a restricted bandwidth so could have suffered.
I have enabled updates using my local network (which only has one Windows 10 machine unless I update my old Windows 7 laptop).