Fixing it is kind of a pain in the ass. I was able to get the hinges off from eBay.
To replace them, you need to remove the cushion on the side of the broken hinge. Then, you'll be able to see the screws (I think they are star shaped) and remove all of them until you arrive to the motherboard.
The hinge is screwed to the headband so unscrew that. Afterwards, you see that in order to take off the broken hinge, you'll need to disconnect all the cables off the motherboard (I highly suggest you to take pictures of the connections before unplugging), that's because later you'll need to solder all of them.
Remove the broken hinge, screw the replacement one, and place the flat cable in the midle, then solder the cables that go to the main motherboard and pass the rest of the cables through the hole so they can go to the speakers, etc.
This part is a little tricky, in order to make the hinge and the part of the headphone to stick together, you'll need to apply pressure to both pieces so they can seal together (in my case I use a little twiser and gently pressed till they clapped).
Continue reassembling, and then solder the rest of the cables. Screw the speaker back into place, and put the cushion back again.
And there you go, you'll have your headphones working as new again. In my case I repaired the left side and 3 days later the right side broke, it's a similar process either way. I was lucky I bought both left and right hinges for like 20 bucks