I had one fail as well, different trailer manufacturer though. You might still be covered under warranty. They sent me both axles that were a new/different design. I replaced the rear axle (no brake lines) in about 2 1/2 hours, I needed to replace it myself even though parts and labor was covered by the manufacturer because I was afraid it would damage the tires and wheel well if I towed it any distance. If its your brake line axle it will take longer because you will need to bleed brake lines.
It sounds just like my situation, as if the splines on the axle jumped inside the rubber housing. You can remove the torsion arm and reposition it to give you the proper suspension travel if you need to tow it to dealer, but you will need to replace the whole axle because it will slip again. I think I asked how much the axles were if I had to pay out of pocket and I think I remember him saying between $350 and $400 each. Good Luck.