Can you give further details about what you mean when you say the "map" is showing upside down, please?
Do you mean the entire display is upside down?
Or just the 2D or 3D view when on the normal driving view (so the other parts of the screen are still in the right place)?
Or is it just the "Browse map" screen?
Do you have the feature on your model where you can set the 2D driving display to either "North up" or "Driving direction up"?
Some newer models have gyroscopic sensors so the display spins when the unit is mounted upside down, but that won't apply to your ONE XL.
Tomtom took away the ability to have "direction up" in the latest XL models. They were sold as XL IQroutes2.
Is that your device (it would have two big navigate/drive to buttons on the main screen). If so, then it is the new "easymenu" lineup which does not support 2D direction up, it only supports 2D north up.