Why won't my ocelot turn into a cat?
Ocelots no longer turn into cats as of the Village and Pillage update where you now get tamable cats from the stray cats that spawn in villages, which stray cat taming works the way old ocelot taming worked.
As for Ocelots now, you can still feed them with fish, however doing so will only make them gain trust with your player (it won't be scared and run away from you anymore), and won't turn it into a cat.
In recent updates ocelots keep their skin when you tame them, this was introduced because you can find stray cats in villages