First of all Sorry Steve that this has taken me a while to post. Family medical emergency kept me busy since we were in contact.
Anyway for the benefit of everyone. Thanks to Steve, I can report my DVSwitch Client app is working fully.
After much pondering and trying of things it was discovered that the issues were at the end of the day not related to the DVSwitch Server and ports firewalls etc. That was proven because Steve connected to the server first time and it worked. So that left me with the t320 and the client to look at.
What eventually was discovered was that after putting a SIM card into the t320 and switching off wifi it all started working, Reconnect to the WiFi directly built in to the ISP router - Again it was now working A OK.
It would appear that the issue was that my main WiFi sits behind a couple of Managed network switches and somehow UDP packets were getting blocked on their way back in.
Honestly I'm at a loss to explain it. However a full shutdown and reboot of my network from scratch to make sure all the ARP tables etc etc were flushed and no I'm happy to report the Client on the t320 is working using 4G, WiFi (my main and ISP direct) also it works tethered to my Mobile Phone.
So there you have it...... Thanks again to Steve!