Check recirculate not on
Posted this before, but in case it's been missed.
Double-check you don't have the recirculate turned on (little circular arrow on display), press circular arrow to turn off. With it on, my windows steam up within a few minutes.
Pressing the windscreen demist button (top right of aircon controls) on my car, even with all windows steamed up, completely clears them within about 30 seconds even when cold. If you press it, you should hear the fans on max and the "Econ" mode (which just means aircon off), should be deactivated.
If this fails, then it may be that an actuator or solenoid is not moving the flaps to the right place and you're stuck on re-circ. Hopefully dealer will read a fault code if this is the case.