I don't know how that happened. I have never heard of that only freze the top row. How do I un-freze it?

What I have noticed is, no mater which section I am in, only the bottom sections are scrollable, so what is the vertical split for?
Are you sure the split is at E23 as this is nowere near the lines. D16, E16, D17 and E17 seem to be in that area.