Hey Carolyn,
Sorry to hear that! Sounds very similar to every conversation I was having, and I know they are doing their best to understand the problem it just has so many layers to untangle.
I ended up having to create new shipping tax overrides for all provinces to ensure the sales tax was still added to shipping costs. We also discovered that some of our odd calculations relating to Quebec’s PST was because of a stray 5% that shopify was automatically added, so I removed the 5% that I had added and now everything seems to be added up correctly. Its so incredibly complicated! Perhaps try the shipping overrides and see if that helps?
My colleague “created an order” in the back end and that is where we were actually able to visualize the exact tax breakdown that shopify was adding to each individual order. Prior to that we had been guessing based on tests on the front end.
I hope you find a solution!