Just to let everyone know, I reached out to Apple through the online process and Apple resolved this!!! I should get a refund in 7 to 10 days. This will allow me to purchase MainStage 3.
Now the plus was that I was able to present Apple with all my details regarding the original purchase and that along with being a n00b with Apple may have helped.
Apple Customer Service was a pleasure to work with and I won't hesitate to engage again if needed.
Apple also supplied me with the following:
a link here with more information about the difference of a software upgrade vs software updates. This is for your future reference.
Software update, upgrade--what's the difference?
Thanks Blueberry for the point in the right direction. :-)