How to address a professor?

I am a student of M.A. in English literature. I study at a university in India. I called my professor Dr. Mukherjee, and he humiliated me and said he was not my colleague. I have learnt from many sources on internet and wikiHow that a student can formally address a teacher with the word "professor" or Mr./Dr. then his surname. My professor's name was Dr. Nayan Mukherjee. I called him Dr. Mukherjee. Why did he get angry? I believe it's very formal. He also said you have to say Dr. Mukherjee sir, which I have never heard in Uk any student saying. However, he also rejected my calling him professor. He said, I have to call him Nayan (his first name) sir, which in my opinion is informal. I saw him a wikiHow article certified by wikiHow quality check team. He answered, we don't always go by Google. I am confused and heart-broken. I want to know whether he is correct or I am. I don't want to learn India wrong English; I want to learn British English. Kindly elucidate.