Following my post (September 29, 2016) I called my ISP. After many efforts I finally got my phone working at home. Here is how that happened.
I followed many pieces of advice from different forums and YouTube. I was so frustrated I almost sold my Lumia 640, and my wife's Lumia 640 and a spare Lumia 530, kept for emergencies. After many hours on the phone to my ISP they decided to follow some technical
ideas and said they would get back to me.
Remember - I could connect immediately with a Samsung Galaxy S4, 2 home computers and my Xbox One - but not one Lumia would connect. No matter what I tried I was unsuccessful.
Eventually the ISP call centre person asked me when I first received my router from them. "It was in 2011", I told them. They said they could find nothing wrong with the technical side of things so they would send a new router - via express courier. Two
days later it arrived.
The router took 15 minutes to set up and all the Lumia phones connected immediately.
There is something in the Microsoft software that didn't like my 2011 router. The software loves the new one.
All issues are solved for me, and I hope will continue to stay solved.