Hello,
Does the device connect to the operator and establish data connection as well as to provide internet access to connected devices?
For one it could be modem related issue, if mobile connection is not established at all.
On the other hand, you are using legacy firmware revision. Is there a particular reason for that? Could you perform an update to the latest 7.04.2, which you can download here?
If the issue persists, I would like you to attach a troubleshoot file to your question. Please, replicate the issue, then access router's WebUI, go to System -> Administration -> Troubleshoot section and download troubleshoot file from there. The logs in the file might provide more insight into the issue.
Best regards,