Based on my memory and this article, there was an old "Microsoft Office" app that was replaced by individual Microsoft Office apps:
However, there are no "Office 365" apps. "Office 365" is a subscription plan that enhances the user experience of individual Office apps with advanced mobile features.
For this particular case:
Samsung Galaxy Tab S2 was deemed as "not compatible" by Play Store. The exact reason cannot be known because there are too many possibilities. However, the download is only prevented on the Play Store. You can still find and download the APK file from credible 3rd-party sources (e.g. APK Mirror) and try to install it, and see if it's compatible (working properly).
Regarding the status of your "Office 365", that depends whether you have subscribed to it or not previously. But the migration from the old Microsoft Office app to the newer individual Office apps didn't affect the status of someone's "Office 365" subscription plan.