How did Hashem speak to Yisrael?
Radak, Malbim: It was via a Navi.
Why did Hashem mention seven salvations?
Torah ha'Temimah citing Bamidbar Rabah 20:5, partially cited in Rashi: I saved you seven times. You should praise Me seven times for this - instead, you served seven idolatries (listed in verse 6)!
Why did Hashem include Amon and Pelishtim? He did not save them from them yet!
Malbim: Just like I saved you from Egypt and the Emori, so I can save you from Amon and Pelishtim. This is why there is no Vov before Amon. 1
Perhaps Hashem refers to previous salvations from Amon and Pelishtim (3:13 2 , 31). (PF)
If so, why are Amon and Pelishtim written in the middle? They should be at the end - just like I saved you from these five, I can save you from Amon and Pelishtim! Perhaps Malbim's words below (refer to 10:12:2:2) answer this. (PF)
Even though there, Amon merely aided Mo'av, who were afflicting Yisrael, Hashem attributes it to Amon, to hint that He can save them again from these nations. (PF)