Why does it say "va'Tizni El Bnei Ashur"?
Radak: El is like Im (with).
Malbim: Achaz sent to Ashur for help.
What is "mi'Bilti Sav'asech"?
Rashi: Because you were not satiated with the To'evos 1 of Egypt. Radak - Sav'asech is a noun. Its grammatical form is like Chachmasech. You were not satiated with the nearby To'evos of Egypt, until you were Mezanah with the distant Bnei Ashur. You desired also their To'evos.
Radak citing Targum Yonasan: Since you did not know Torah.
Refer to 16:26:2:3*.
What is "va'Tiznim"?
Rashi: It is an expression of Zenus. Radak ? you were Mezanah with them
Why does it add "v'Gam Lo Savata"?
Radak citing Targum Yonasan: You did not even know Teshuvah.
Malbim: "Va'Yavo Alav Tilgas Pilne'eser Melech Ashur va'Yatzar Lo v'Lo Chazako" (Divrei ha'Yamim II, 28:20).
