Vw passat electric trunk won't open even with the key?

If the actuator cable breaks then the key and the interior release both don't work. It needs to be replaced. If your trunk has a manual release inside then you can pull the back seats down and reach in to release it. Then undo one screw in the interior handle and pop out the plastic covering on the trunk. Then you will be able to see the cables. Good luck. Check out YouTube.