For some reason Premium credits are not listed on the uplay store and access the credits section in-game gives me an error saying "The Store is Empty"
I'm sorry to hear you all are having this issue. Please install the latest version of Uplay and run it as administrator. Let me know if that helps.
I've just checked my Store tab, and I see the content. If you could provide a screenshot of what you see on your side, that would be great.