Ok. First, I want to thank those who tried to assist. I have finally discovered the problem....... It was the phone itself.
I eventually organized myself and set up a troubleshooting tree, which I then followed. The most important part was using my daughter's Lumia 920 in place of mine. And wouldn't you know it, when I unhooked my phone from the Surface Pro and put her phone
in place of mine with same cable and set up...... It worked fine. So I now surmise that there was something funky going on with the USB connection of that phone. And yes, it appeared correctly in the device manager.
Convincing the guys at the ATT service center took some doing, though. The first guy did not really understand what I was telling him and he kept looking for some way to fix it in settings.... Finally a manager came up front and I demonstrated the problem.
He got another Lumia 920 and plugged it into my surface and -gosh- it worked. He was convinced. 10 minutes later, I walked out with a new phone.
Can't imagine what this whole process would have been like if I had to do that over the phone and by mail..........
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