High Off Peak Data Usage?

[#1]

I have just checked my data usage for this month and I somehow have used over 1Gb data off peak on Thurs, Fri and Sat (most of it classified as streaming). The thing is that I've been in bed before midnight each night so haven't been actively using the Internet off peak, Sat night I actually turned off WiFi on my laptop and still used over 200Mb of  off peak data!
Has anyone else experienced similar unexplained high data usage?
I do watch films and TV series via Netflix but never after 10pm, I am concerned that even though I am unlimited broadband my usage will be classed as excessive, I have used 13Gb since 15th of the month (the start of my 'month'). Any idea what is deemed to be fair usage?

[#2]

You're in no danger. So far this year I'm averaging 135GB a month, and there are no doubt a considerable number of users using far more.
Unlimited means just that. 

[#3]

OK .. thanks for that ... I'd still like to know why I have such a lot of off peak data usage though!

[#4]

Do you have a suitably strong wifi password? Could someone be using your wifi? You could always switch off the wifi on your router when you finish using the connection.
Don't forget that usage figures are delivered after the fact, and inevitably some data used before midnight won't be received until after midnight, causing it to be classed as off-peak.
Don't forget also that many devices such as smart phones and tablets download updates when you connect them to the wifi, and if you leave something switched on and connected they can add to your usage without you knowing about it.

[#5]

Thanks for the pointers .. I will make sure everything is switched off and see what that does.

[#6]

Peak and off-peak usage shouldn't get mixed up no matter how long it takes to update the VMBU display. Also Plusnet discard usage information covering both peak and off-peak periods to avoid peak usage being overstated.
If you login to your router (assuming it's a Plusnet supplied one) and go to the Home Network page here the Wireless section at the top should list all devices that have connected to W-Fi since last re-start. Are you able to identify all those devices?
Further, have you passed on/sold a previous Plusnet router which might still be connecting to your Plusnet account?

[#7]

Thanks for the information and advice. I haven't sold or passed on an old router. I checked the devices listed and there are a couple of unknowns, however when I searched the Internet for the physical addresses they appear to be Samsung related which is probably my Daughters device. So far as I can tell there are no unknown devices connected.
Is there any way that I can identify data usage by device?
Thanks for your help

[#8]

To provide central moitoring you'd need a much more expensive router. So device level monitoring (where available) is the only option.
Windows PCs can be individually monitored using (for example) NetWorx - which supports consolidation on one machine if desired.

[#9]

Thanks .. have downloaded Networx and WiFi monitor.