Follow your polite 'Excuse me' with a neutral 'Can you please step out of the way' followed, if needed, by a sharp 'I have to be where you stand now'.  
If that does not work, get rude and push.

When leaving trains I will never ask, I just walk out.  
Elbows out if there is not enough space for two people at a time.  
And aiming (if not to harsh) for body parts for those who stand in front of doors.  
If carrying a bag on a shoulder strap that will be in the same position, elbow to middle of the body.  
(But I am a rude Dutch person who does not appreciate being stuck in a train while people crowd and block the exits.)