My professor says I would not graduate my PhD, although I fulfilled all the requirements


I am a Ph.D. student at a university in Germany.

After about four years of research, my supervisor told me to write my thesis. After I sent him my thesis, he told me that he now thinks my work did not have enough scientific soundness and that I would not be graduating anymore. I published more than eight papers with him, including international journals and conferences with him, and worked as he suggested.

One year before, he wrote me saying I had enough material to write a thesis, so I should start writing, and now he is 100 percent the opposite. His behavior is so bossy now that he won’t hear whatever I say. Even the other professors can not challenge his decision because of their personal relations with him.

Should I take legal action against him based on his previous and current statements. If not, then what could be the alternate way?