The first thing you need to do is replace the worn hinge. You have likely bent or broken the latch mechanism from continual slamming of the door to close it. Try using a screwdriver to push in on the latch and see if it will click in place. The pull the door handle and see if it will release. You could have bent or moved the part attached to the car body. Everytime the door hits the latch it likely disturbed its original location. You may need to adjust the striker back to its original position. Check for signs that the striker moved by looking for missing paint.