Have I been sleepwalking ?

[#1]

Have I been internet trawling in my sleep ?
It would appear so, because for the last three months my off-peak usage figures have been June 535MB, July 2.42GB and August 25GB.
This is all very puzzling because having the appearance I have, I need all the beauty sleep I can get and am always in the land of nod between 12 midnight and 8 am.
My two computers, desktop and laptop are always switched off during this time.
'So it appears that either Plusnet have messed up or someone is somehow using my connection.
I have secure passwords and pass-phrases on my router and computers and a good internet security suite on both my PC's.
Of course I should be asking this question of Plusnet themselves but the phone waiting time is astronomic, and when I try to post a message on the help system it tells me I have 160 characters but the remaining characters reduces to zero after I have typed about 40 letters.
I did wonder why so many people were expressing dissatisfaction with Plusnet, now I know why !
Time to start looking around methinks and pay out a bit more.
Any ideas anyone and does anyone from PN still read this forum ?

[#2]

Just a thought. Are you running Windows? If so, have you upgraded to Windows 10? This may account for some of the usage but not it all. That's a lot of unexplained traffic. What does your usage report as?
P.S. You may want to get to bed earlier. 

[#3]

I have recently updated both my machines to Windows 10 but this was all done during peak connection times. Both machines were switched off during off peak times and they are not set up for internet wake-up.
I guess from the remark about even more beauty sleep required,  that you must know me 

[#4]

No, I don't know you, but lets put it this way, I'm in my bed for 21:00!
What does this tell you : https://portal.plus.net/view_my_broadband_usage/index.php
I"ve used 41GB peak and 2 off-peak with most of it being streaming!

[#5]

That's the pages I've been getting my history information from.
I do very little streaming but the Windows 10 updates for 2 machines did use about 75 GB of my ON PEAK allowance (unlimited). It's the mystery overnight usage I'm worried about.
I'm usually counting sheep by about 10 pm, I told you I need a lot of beauty sleep

[#6]

Well I think that can only be answered by someone from Plusnet, with a bit of luck they'll be along soon.

[#7]

Windows 10 uses some kind of peer to peer functionality to distribute itself and this is on by default. Could this be the cause?
http://www.pcworld.com/article/2955491/windows/how-to-stop-windows-10-from-using-your-pcs-bandwidth-...

[#8]

...but the PCs are switched off

[#9]

These days I'm not confident that our definition of 'switched off' matches Microsoft's version

[#10]

@oldgeezer
I've checked and there's nothing that jumps out at me. Nobody else is connecting with your details and the usage is definitely coming from your line although we can't see what devices have been using what.

[#11]

Is the op sure that nobody is leeching and using his wifi, wifi passwords are very easy to crack these days which makes it very easy for someone to leech onto your network. I suggest downloading  something to monitor your wifi connections. Something like who is on my wifi, is free and will show all connections to your wifi.

[#12]

I checked to see if the Windows re-distribution flag was set and sure enough it was set by default on both PC's. It isn't any longer.  That still doesn't explain how the usage mounted up overnight when the computers were switched off.
However I think I may know what's happening. I have a small 2 disk NAS permanently connected to my router, A Synology 214se.
A couple of weeks ago I came down to make a cup of tea about 3 am one morning as my wife couldn't sleep. I glanced into the room where the NAS is sited and it was lit up like Blackpool with the disks whirring. I assumed that it was updating itself but I now know that it is scheduled to do this at a different time.
The Synology doesn't use a Windows operating system but my main PC does back up to it. I've just had a look at the Synology log and sure enough on several nights there is an entry reading "System Started  (Windows File Service). I've looked on the NAS files for anything suspicious and can't find anything, but there again we are talking about Microsoft 'so I wouldn't would I.
It's too early to tell but the Mega Big overnight downloads were back down again last night.
If they go back up again I will set an overnight internet shutdown on my Billion router scheduling.
Thanks for all your suggestions.
Regards.