this kind of thing never gets better in the hub. eventually they may stop targeting you but don't get your hopes up. what you need to learn is what to say.
It's good you know some of your rights. But much like your rights when under arrest, you have to say certain things to invoke your rights when management is bothering you.
"Where's my steward?"
"Do you have proof that I did those things other than what one member of management claims?"
"You have to train me to do this if you think I am not getting better at it. And to train me you need to show me, step by step, instead of just standing beside me and throwing things."
And never, ever sign anything unless your steward says to.
If you are ever pulled into a room to talk to a FT sup or a manager, ask for your steward. Demand it. If they don't have the steward in the room while they talk down to you then you immediately file a grievance or just walk out of the room.
Trashing your load is not something I would suggest. Not only are you damaging the packages but you are probably hurting the unloader who is going to unload that trailer. When I was a trainer in unload, the most frequent injury was messed up walls falling on people or hidden heavy objects jumping off the tops of bad walls.
If you go slow and do your best and you still don't get it, you need real training or you are hurting your teamster brothers.