Cannot access Emby outside home network

[MrGiles 2]

Since switching ISP and installing a new router, I have been unable to access my Emby server away from home.  I have gone through all the recommended troubleshooting and as far as I can tell everything is set up correctly, but outside my home network I just get the message 'unable to reach Emby NAS'.   I have the same connectivity issue on the Android app and on my laptop.  I'm running Emby server on a QNAP NAS, and I can still access the NAS remotely, just not Emby.  

Any help or suggested further steps would be appreciated, as I'm no expert on network settings