From what I can tell, cellular data shouldn’t have been detected if cellular was disabled. With that in mind, the following excerpt causes me to question it.
“If you use an Exchange ActiveSync account, it might continue to use cellular data even if you turn it off for Mail and Calendar. To see the cellular data usage of your Exchange ActiveSync account, go to Settings > Cellular > System Services.”
Source:
https://support.apple.com/en-us/HT201299
I know it’s regarding the disabling of cellular usage for Mail & Calendar, but I’m wondering how is it bypassing the blockage, and if it can bypass that, could it or something else be bypassing the overall cellular data block?