I want to first say thank you for this site!
In my case the handle on the back door snapped and it was a lever that goes in the door that broke off the handle.
This lever goes through the door and pushes down on a lever that pulls the cable that opens the lock.
So if this is what is happening you are going to be able do make "a small hook" from a piece of semi sturdy metal and push it through the hole for the lever and "find the lever on the inside" (this may take a little patience and intention) and push down on it.
This will open your door without having to open up the panel from the inside.