We have got a Es440 gateway for one of our clients for remote monitoring because internet was not available. The gateway works nice but for some reason we cant ping its public ip nor connect to it via ddns. Attached to it is a surveillance system that the client wants to monitor remotely.
Are you sure that your sim card has got a routable, public IP Address? Most if not all mobile networks use NAT to provide Internet connectivity to devices - which means that you cannot talk to the device until it has established a connection to your server.
I suspect that ddns is getting the private address of your modem which cannot be routed to. This is why you cannot either ping or connect to the device.
Can you check the IP address that ddns is getting for your Device? If it starts with 10., 172.16…, or 192.168., then you have a device behind a NAT gateway. If this is the case, then you’ll have to go to your mobile provider and see if you can get on a sim plan that will provide a routable IP address.