If you want to access the SSH CLI of the router trying to connect through a public IP or in this case using a DDNS service you have to enable a feature called "Enable SSH access" option. To find this option first click on the System tab on the left side of the UI, then select the Administration menu and click the "Access Control" option. On that, you will find that feature and that feature is going to let you connect to the device through the public IP or in this case the DDNS service.
At this link, you can find more information about this menu: https://wiki.teltonika-networks.com/view/RUT240_Administration#Access_Control
Please try again the configuration for the DDNS service, at this link you can find a configuration example: https://wiki.teltonika-networks.com/view/RUTX_Noip.com_DDNS_configuration
Also please verify that the configuration of the DDNS on the side of Noip is working properly.
Please verify the IP that your device is getting, sometimes mobile providers could be assigning private IP's because of the APN that they are using and with a private IP it would be impossible to connect to the device remotely.
This should fix your issue.