I agree, but this quote from the OP makes it quite clear:
"On boarding we went straight to the desk and asked why. We were told that our new cabin was larger and therefore an upgrade"
It's obvious what they did wrong. Research your cabin all you want, but also understand the terms you are accepting when you book. I don't recall if "No Upgrade" was the default, or if I had to click it when I booked, but in either case, you need to pay attention to what you're signing up for.