You should find the line style and fills under contour -> geometry -> DisplayFilled, Filled and LineStyle.
The colors are somewhere under ActiveView -> DisplayControl -> GeneralItemsColor
When I display these properties DisplayFilled he said False and Filled also false while the contour is not filled
Linestyle is 0
I am lost now
I just tried it. The geometry properties are readonly and there is no way to fill a contour (as far as I can see).
So the next thing, you should check: Is the contour property "Hole" correct. Or check, if it is really the contour, that is filled and not any other object with the same dimensions. The property window for the contour should give you the same information and you don't have to use automation.
some of the geometry objects can not be set to filled or unfilled (such as placement outlines too).
But you should be able to define a display pattern instead, where you can select the unfilled one.