Leacky caldroun (black door next to tapas restaurant)

After shifting to the Hogwarts I was so curious to know more about magic and wizardy world then I found this place(HIH) after sending messages to the proffesor and they keep telling me is all fictional and for fun ,they even denying my parallel self shifting experience to the Hogwarts and that extremely unique experience,I felt one of those proffesors had the balls to talk about the truth and existence of wizardy world that even he played with me in the end,now even if that non-script black door is the entrance to the leacky caldroun ,how could I enter when street is extremely crowded and I was pushing the door and even behind that door was an empty space,that proffesor said I should send the ministry a letter by an owl ?how can I send when I don't have an owl and not enough time to buy when I was in London!!is that black door on Charing cross road really entrance to leacky caldroun and if yes how one Muggle born like me could enter,is it portal???