I know for certain that there is one person who has achieved this lofty state of Nibbana. May I for now call him Ven. Jahn Galt? John Galt is a character in Ayn Rand's novel Atlas Shrugged (1957). Although he is not identified by name in that novel until the last third of the novel, he is the object of its often-repeated question "Who is John Galt?" and of the quest to discover the answer. What is important here for you and I, is that this Ven. ‘Jahn Galt’ who is an Arahant can show you the correct way. For example one correction I will make here. It is not ‘Nirvana’, but ‘Nibbana”.
Nibbana means freed from existential captivity or having existential relationships extinguished. The antonym is samsaric captivity. One who is captive in the circle of raga, dvesha and moha creates own existential relationships for survival and goes adrift. All three binds of captivity are like strings woven together (bāna) causing samsaric existence to continue. Nibbana is the outcome of eradication or uprooting of all three strings of the bāna.
For your next main question, YES, the 'Buddhism' that is known to us in the present day is CORRUPT. It is high time that this corruption is shown as there can be at least one or two of you can then attain Nibbana in this very life.
As expounded by the Buddha, the Buddha Dhamma that discusses the noble path toward the attainment of Nibbana is known as Patichcha Samuppada Dhamma (pati – bond; ichcha – desire; sam – 3 fetters – lobha, dvesha & moha; uppãda – arise). To comprehend the four immovable truths (chatu ariya sachcha), the knowledge of the Patichcha Samuppada Dhamma is indispensable. Gaining of true penetrative wisdom, to grasp the reality of life (or existence) as it is (yathābhuta gñana), is possible only through full comprehension of the four immovable truths. This is not about gaining the full extent of theoretical knowledge or learning but rather, attaining a penetrative deep experience that exceeds the dimensions of conventional wisdom while transforming one’s attitudinal inner view on life/existence.