1. Please make sure you really have the internet connection on your RUT950. You can go to CLI, log-in with root and your webui password and use ping command to see if you're able to reach WAN network. ping 126.96.36.199
2. Check if you don't have any VLAN configurations done before, I would highly suggest resetting the device to factory defaults to avoid that.
3. Check if the cable connected to your RUT950 and computer is fine, try a different cable.
4. Make sure your network card in the computer is not preset with static IP, gateway and the subnet. It could be that it's not set to automatic and doesn't get the IP it needs. Also, you can add 192.168.1.1 (router LAN IP) as a primary DNS server for resolving issues.
5. Try different SIM cards.
6. Try different LAN ports on RUT950.
7. Try a different PC.