Passat door handles from that era have a pivot pin that tends to work it's way loose, so that when you pull the handle, the part inside does not move far enough to press on the lever that releases the latch. What you can try is either sliding the entire handle assembly toward the rear of the door, or holding the non-moving "thumb button" portion of the handle hard against the door, while pulling the handle. There is often a lot of slop and free play in the handle, and doing what you can to eliminate that may help you get it open.
Once you get it open, (the first thing you should do is deactivate the child lock) remove the phillips screw on the rear edge of the door that holds the latch in place. You won't be able to fully pull it out, because there is a wiring harness that connects to it, but you should be able to see where the pivot pin is sliding out or missing. It can often be replaced with a screw that fits tightly- simply reseating the roller pin won't work, it will slide out again soon. Another thing that can be done is the "plate" that is on the latch lever inside the door can be bent or adjusted upward for better contact with the "finger" on the handle mechanism.