Right-click on the axis, and choose format axis – new pane pops up (at the right, or maybe floating) – does changing between a text axis and date axis help?
I can’t quite work out from the description if that’s the problem though – sorry. Can you post a screen shot?
Edit: yes I can, I’ve just discovered that if you have names of months (e.g. oct) it behaves differently to if you have dates (e.g. 01-Oct). However, the number format/display might be ambiguous. The fix above works for date-formatted cells, toggling between date order (months in sequence) and text order (as per your list).