Have I wronged someone whose asking price for his house provoked me, so I mocked him, and he then uttered a harsh supplication against me?

Both of you are unjust to the other. You wronged him by mocking him, which is forbidden by religious law, as stated in the Almighty's saying: "O you who have believed, let not a people ridicule [another] people." This is also because mockery is an act of the ignorant. And he wronged you by supplicating against you, for the supplication of the wronged against the oppressor is permissible only to the extent of the injustice, and no increase beyond that is allowed.