CFC concentration in the atmosphere has only gone down since the Montreal treaty so it's still a success so far. (edit: I should have said "since 2000", the treaty was a phase-out to zero emissions by 1996)
What happened was that the rate of decline of CFC concentration slowed down[1] after 2012. This was an indication that there were new emitters. China then found the emitters and shut them down. [2]