On my Samsung J3 smartphone I have BT Cloud set to use WiFi only. I have no photos stored on the phone, I have music stored on my SD card but that is set not to backup. At home my BT WiFi is on all day but is off (through Power Saver) overnight.
The day before yesterday, though I don't know whether it was during the day or overnight (and I was at home throughout), BT Cloud suddenly used about 250 Mb of mobile data which is half my monthly allowance. Frustratingly that was just 1 day after my allowance reset.
Has anyone any ideas as to why that could have been?