What is the device code and current Firmware version?
Try to reset the device and check if issue persists.
As the device is not physically accessible I would recommend to reset it via the RMS platform.
You can also try sending a SMS to the SIM number or a command via SSH. Just keep in mind that with these 2 last options you might lose connection to the public IP address.
SMS: Send "<router_password> restore" to the SIM number.
SSH: Connect with Putty or similar to the device. Log in and type "firstboot + ENTER". Confirm the prompt question with "y" and send "reboot + ENTER"