This is just a guess, but it looks like when you add another layer of data and then create a dual axes, you have labels in both layers.
You should have multiple "sheets" that are laid on top of one another, and you can change the labels on each of these separately.
Click on both categories/divisions, and make sure the "Label" is blank in one of them if you are expecting them to overlay.
See if this solves your problem. Good luck!