I just fixed this on my 2016, and the solution was different than any of these other answers. One day (not below freezing), the charging door stopped opening, and none of the "Fonzi bump" solutions offered worked. Finally I decided to take my chances and pry the door open, got a chisel in the gap, and it popped right open. One can slide the colored cover off by working it to the rear, so I did this, careful not to break any of the tabs. At that point I could charge the car, and if the door was accidentally closed, I had access to the latch and could pop it open again.
Now I opened up the charging area: first I loosened the rubber gasket enough to get behind it, and then slid off the little assembly with the latch: the "Door Lock Actuator." Although it was tethered into deep inside by an electrical cable, I was able to get it out of the car enough to look at it. I destroyed this piece by prying the lid off, but that turned out to be OK because the actuator was a mass of corrosion. And that was how I learned what happens when you park the car outside 24/7.
This piece is available; I got mine from Car Parts (Part no RB746403) for $41; it arrived in 4 weeks.
Replacing this piece was devilish, as it plugs into the electrical system, so I had to pull out the back trunk cover and the get the side trunk cover out of the way as best I could. Then it took about 2.5 hours of awkward work and cussing to get the piece replaced.
Everything works now, I now park my car in the garage no matter what, I paid $41, and I spent about 4 hours on the project.
