Who was Chananyah ben Azur?
Sanhedrin 90a: Initially he was a true Navi. At the end he was a false Navi.
Radak (1): He was a false Navi.
Why did he say "Shavarti"?
Malbim: I already broke Bavel's yoke on Yehudah - the opposite of Yirmeyah's Nevu'ah that Tzidkiyah and the other kings must accept the yoke! In two years (verse 3), I will break their yoke on the exiles in Bavel.
Why did Chananyah err to say so?
Rashi (1, citing Sanhedrin 89a): Chananyah heard Yirmeyah prophesize in the upper market "I will break the bow of Eilam" (49:35), and [based on this] Chananyah prophesized in the lower market "I will break the yoke of Melech Bavel." Chananyah made a Kal va'Chomer. Eilam (Madai) only came to help Bavel (afflict Yisrael), yet Hashem will destroy them. All the more so He will destroy the Bavliyim themselves!