climb in from the other side and try the handle from the inside? unless that glaringly obvious and you've tried that already?
I have taken the door cards off in the past, and found that the little metal rod that links to the internal handle is a very simple connector. you have to rotate the plastic clip and then the metal rod (like coat hanger metal) pops out easy as anything.
not sure if it would affect the outer handle but if the inner one not working, start looking there I guess. should at least be able to get the door open which is obviously necessary to get the door card off
not having done anything with external handles I cant advise much other than get the card off and have a look. and good luck. take pics and post if you can't see what's going on, someone else might spot it