Where does all that matter go when it is pulled into a black hole? The most scientific theory at the end of the day is still a theory.
The outer rim of the black hole has such a strong gravitational pull that anything that gets caught begins to break up. I suppose it could be described as mushing down a planet into soup.
There are however some weird and interesting theories of what are inside a black hole and it really is open for anyone to speculate. My favourite is that inside the black hole is the entry to another universe. Perhaps we can visit our parallel self.
Black holes are a wonder and until we invent the ideal equipment to truly know what these holes lead to it will remain an interesting question.