Sicily 43 DAR (No peeking Herr Antoni)

[Currahee]

Mobile-type units are unable to attack into badland hexes (and the hill hexes you're having trouble with are probably also badland); this is due to their mobile equipment, such as trucks etc. Only straight, non-mobile infantry can attack in; or HQ's or arty, which actually used ranged fire to attack the hex. It is possible to finally eliminate those enemy units, with HQ's and artillery only, alto it may take a bit of time.

Above is also true of Alpine, I don't have the scenario in front of me, but looking at your screen capture, Alpine may me the culprit there, as well as badlands.

This is really a designer issue; the badland and Alpine hexes must be used selectively, they absolutely prohibit movement to mobile units, and in the case of Alpine, I believe all movement is prohibited, except along roads or trails.