GM/Cadillac is the same thing. Cadillac is just a brand made by GM the same way Chevrolet, Corvette and GMC is made by GM.
My question is what happened to the car? Are you saying that you defaulted, but GM does not want to repo the car? Yes the lien is still valid. If you want to get a lien release you have to go through Cadillac if they are now the lienholder.
There are other ways to satisfy a lien but Cadillac is still in business so there is no other way to get the lien release than for you to make some kind of agreement to get the car loan paid off.