You are using the same Microsoft Account? You can email their support with a copy of the Billing Confirmation Email that Microsoft sends with every purchase...
Yes, I haven't changed my account but I did do the free Windows upgrade that was offered a couple of months ago. I think that's when the issue surfaced (so to speak ;-). The OS upgrade was not as transparent as I imagined - a number of my settings required fiddling with.
I've never interfaced very well with Apple computers - they seem overly simplified to the point where usability suffers. I can never figure out how to make changes so it works the way I prefer. I'm afraid this new touch screen Windows is one small step in that direction. It just feels nebulous.
Update: I figured it out. Apparently the Credit Card I had authorized on my MS account had expired and I had not entered the new card number. The MS store had tried to charge my card five times over many days but kept getting denied. Eventually the app stopped working (without telling me it was due to a billing problem) and I uninstalled it and tried to re-install it (unsuccessfully). All this without any notification (by e-mail or otherwise that there was a billing issue).
Thanks for all the help, the problem is resolved.