I also tried to create a text box and put it next to the y-axes scale bar as an alternative. But my difficulty is how to make it in vertical format.
I don't see a difference. Can you check if this is what you want:
I have attached the sample for you to view as well. The only thing to note here is that you can move the Text in Chart (can be calculated expression as well) to move around to place it anywhere you want. To do that, you need to press Ctrl + Shift and you will see red lines around the text in chart. While still pressing Ctrl + Shift, move your Text in Chart to your desired location (near y-axis) and you are all set.
If this is still not what you are looking for, then please let us know.
I don't think there is such thing as a Y-axis label, but the 'Text in Chart' as described by sunindia works in exactly the same way. The 'angle' option is the way to make it vertical (either 90 or -90, depending on which way you want it to face)
You can also put code, as well as text using the 'Text in Chart'.