1)
Why did He need to say "Hispalalta Elai"? Obviously Chizkiyah prayed to Hashem!
1.
Malbim (Yeshayah 37:19): Your Tefilah was primarily for the honor of My name.
2)
What is the meaning of "El Sancheriv"?
1.
Radak: This is like due to Sancheriv.