Should i start a legal case now because it's been 2 and a half years, or let my union continue their process? Or is too late?

I was awarded a bid to be a Maintenance Mechanic Apprentice. I was supposed to be given a year to train, but they put me back to my original job after 3 months. My supervisor was supposed to be giving me reviews and information, but because i didn't get them, I wasn't able to answer my company's questions about what i learned correctly. Regardless, if i was incorrect they were supposed to help me, not demote me, at least until the one year mark. My union has been working with me, but it has been 2 and a half years already.