1)
Why does it say "Ach"?
1.
Malbim: The salvation was not via Teshuvah (rather, like verse 7 explains).
2)
Why is there no Aleph at the end of "Hecheti"?
1.
Radak: We find like this - "va'Shem Chafatz Dak'o Hecheli" (Yeshayah 53:10).
3)
Why was the Asherah still in Shomron?
1.
Radak: Yehu destroyed only Ba'al.