[USB tethering] Windows eats up my data plan

Hello,

I noticed a problem that I already had on Windows10 and experience again on Windows11 to which I migrated months ago: After connecting my Android phone to Windows through USB tethering and sharing its memory (ie. file transfer mode, not just charging), Windows or some application mistakenly use that Internet connection instead of going through the fiber connection. As a result, it eats up my small 2GB data plan, and I'll have to do wtihout until the middle of next month when the reset occurs :-/

Has someone also experienced that problem? Is there a way to know if it's Windows or some specific application that takes the wrong route to the Net?

As a temporary fix, I'll have to always remember to turn off the data connection before connecting the phone through USB in file transfer mode.

Thank you.

I think there’s a small mix-up between two USB modes.

File transfer (MTP) is just for copying files/photos or charging — it doesn’t use mobile data at all and can’t give internet to your PC.

USB tethering is something different: it shares your phone’s mobile data with Windows and turns the phone into a network connection.

So if Windows is showing data usage from the phone, it pretty much means USB tethering was turned on at some point (even briefly). File transfer mode by itself can’t do that.

Sorry for the error. I meant that some application goes through my phone instead of fiber to rech the Net when I turn on "USB tethering" with the phone physically connected to the computer.

It's your Phone settings not Windows.
This is for my Samsung:
Settings > Connections > Data usage > Mobile data > OFF.

It is that which really matters, not your USB or WiFi connection mode. Mine is currently connected by WiFi and USB but zero mobile data usage.
Mobile Hotspot and Tethering is entirely greyed out(unavailable) on mine, as it should be.

You should never need to turn on USB-tethering on your Phone when transfering files/images or charging your phone. When I connect my Android phone to my PC, I see a popup window on my phone where I can choose between: File transfer, image transfer or charging.
I am connected to internet by Mobile Data only (my current data plan:108 GB/month), that's why I use USB-tethering.