If you have automatic upload set up, to back up your data to OneDrive, this can use your connection, to send screenshots to OneDrive!
For a complete list of consumption:
> Open Windows settings
> Click on "Network and Internet"
> Click on "Status" on the left side menu
> Click on "Data usage"
You will see the complete list of consumption! I apologize if you have already taken these steps.
If you need any help, write again!
I wish you the best!