Thanks for the suggestions. I tried changing to the 3G setting but the modem doesn't pick up the ISP network. I haven't tried setting a data limit, because I don't think this would fix the problem below...

 

In an attempt to find what was using all the data, I powered down all of the connected devices and saw data usage was still creeping up by few Kb per minute when no devices were connected to it, so after roughly five hours the modem had clocked up more than 20Mb mobile data with nothing connected! When I reconnected an iPad to do a basic Google search and visit 2 websites, I saw the data usage quickly jumped up by another 60Mb for online content that should have used a few hundred Kb's at the most.

 

I have used SIM cards from 2 different ISP's in the modem and there was an inexplicably high amount of data usage on both of them when accessing online content that should have taken a fraction of what was used.

 

It is obvious that something on the new tp-link modem is causing this issue and I'm at a loss as to what to do next... apart from going to the shoreline and flinging the bloody thing as far as I can into the sea!

I am also getting tgis problem. First time using yesterday, watched about one hour of normall tv and used about 500 mb. This cant be right. Ive got a ee sim with 120gb to last a year, lucky if it lasts a month!!! Think it could be going back.

Update: I switched my parents back to using their old Huawei 3G modem which is locked to a service provider (Vodafone) and had to pay $150 for 75GB of data, because their account balance had been drained to zero using the tp-link 4G LTE... Guess what... when we reconnected with the 3G modem and data SIM that previously used to use about 50Mb per hour, we found that it is now using data at the same inexplicably high rate and burning through roughly 500Mb per hour for basic web browsing!

 

Obviously, the disconected 4G LTE modem can't be causing this to happen... but the problem only started when I switched the Internet service to run through the 4G LTE modem  so IT MUST HAVE DONE SOMETHING to the Internet service or conected devices that is now causing them to continue consuming mobile data at a massive rate through a  different modem.

 

Technical support hasn't been any help and doesn't seem to understand the problem.

 

All devices have been set to low data mode with background apps switched off, auto updates have been disabled and the wi-fi network is password protected (so no unauthorised users are tapping in). No streaming services or video content is being viewed and internet usage is pretty minimal (just email, browsing the web and going to sites for news, weather and sports results etc.)

 

None of this makes any difference and data usage is massively high for the type and amount of online content that is being viewed.