Nissan P12 wagon rear door stuck

Hi Adam. Have both handles failed? inside & outside. 

Try downloading the Free Service Manual from here.   That should give you some idea of what to look for.

I managed to fix it. My hunch was that the child safety lock was on (hence the inside handle not working). Combined with a sometimes failing outdoor handle resulted in this situation. I opened up the doorpanels on both rear doors (after taking out the seat). I used the open door as a reference to see where the child safety lock was located and what the on and off position were. Using the camera on my phone to look inside the door I managed to locate the lock mechanisme on the closed door and flip it with a large screwdriver.