Sliding closet doors keep coming off the track, how to fix

K Charles wrote:
You just need something on the top of the door so it won't go up. Just a small piece of anything right next the roller.

Yes, something like a metal corner brace cut to size. Could be attached on the inside of the closet on each door. The part of the corner brace that would ride under the track would need to be cut no longer than the width of the door. I would put two on each door at the ends of the door. Should completely stop the door from raising.