Since we know white dwarfs are made of electrons and neutrons stars are made of neutrons and quark gluon plasma. What can we say about the black hole in this sense since its properties are far stranger to any object in the universe? Can we say it is made of some exotic particles which we don't know of yet?
We don't and can't know what form matter is inside a black hole.
We can take an educated view of what form the matter is in as it crosses the event horizon, but after that its fate is hidden.
Using General Relativity, it gets squashed to an infinite density at the central singularity - presumably passing (very briefly) through similar phases as exist inside white dwarfs and neutron stars as it does so.
However, nobody thinks that GR is the last word on this matter and some sort of quantised gravity theory will be required to describe what actually happens. Whether or not such theoretical predictions will ever be testable is speculation.