I noticed charges on my CC for the duration of the time I had actually disconnected the device from Raspberry (to download some apps and upgrades) and was using my home wifi.
Steps to reproduce:
1- Disconnected the device (physically remove it) from Raspberry pi
2- Connected to home wifi
3- Check sixfab dashboard for the data usage for your device and save screenshot
3- Downloaded apps and upgrade Rapberry packages
4- Check sixfab dashboard for your device after an hour where you will see charged amount
Note that by doing above steps you will lose money depending on the downloaded data