Dying Cambria

[Cambria]

This is my first post on this forum and, unfortunately, not a very happy one.
I few years ago, I bought a very beautiful Cambria, on a local supermarket. It is my first orchid. So, I probably didn't care the plant on the right way.
It was getting several new plants, and the main pseudobulbs were dying of. So, I decided to separate the good ones from the bad ones. To do it, I needed a new pot and something to get the plant into. I decided to buy a bag of what they called orchid soil. It turns out that it was more soil than more coarse material. Unfortunately, I didn't know that this soil would be bad for my orchid.
After a couple of months, everything was dying. So, I started to google on the subject. It turns out that it wasn't a good substrate for orchids.
Now I got a new substract and the new pseudobulbs are happy now, with new pseudobulbs and several new roots growing.
Now I am worried with my old orchid. Even being on the new substrate, they keep looking not good. The roots are rotten.
I need advice on how can I make it to get new roots. The bagging method should work?