WiFi Calling keeps dropping out

[#1]

I have a Lumia 640 mobile working on EE with WiFi Calling enabled. My Plusnet router is a Sagemcom 2704N connected to fibre BT modem. The phone initially connects to the WiFi calling but frequently drops the connection needing a phone restart. Is this a router configuration problem, any help appreciated as I have been struggling with this for 14 months. Works ok with my son's Sky router and my daughter's Plusnet copper router.

[#2]

plusnet routers are garbage thats why they give them away You would be better off buying your own router when u can afford too.

[#3]

I too am having problems with WiFi Calling, I upgraded my phone so that I could use WiFi Calling as I have no signal in the house. I have a LG K8 on EE and the house router is a Technicolor T582n. Over the past week I have searched for a solution to this, it does seem (especially for iPhones) that you have to have different SSID names for 2.4GHz and 5GHz channels (although I am unable to find this information in the routers configuration panel) but it does seem that the 5GHz band is not broadcasting... then I stumbled across this article...

https://woodygems.wordpress.com/2014/11/11/a-fix-for-wifi-andor-lync-drop-outs-in-windows-8-1-and-wi...

The end of the article is the bit that I am interested in I'm not sure if it's related or not but I'm going to give it a try...

Any other suggestions would be welcome.

[#4]

Tried the options described in the above article... neither worked for me, so it's back to the drawing board...

Any ideas what to try next?