# why are you angry at me ... Philistia?

"you have no right to be angry at me ... Philistia." 

# Will you repay me?

"You think you can get revenge on me, but you cannot." 

# I will immediately return your repayment on your own head

"I will cause you to suffer the way you wanted me to suffer when you repaid me"

# repayment

This refers to Yahweh harming those who have harmed him, not to him giving them something good because they have done something good for him.