Will the supplication of one who supplicates or says "Hasbunallah" (Allah suffices us) against another, believing that the latter has wronged him, be answered, while in fact the one supplicated against did not wrong him?

Cursing an oppressor (invoking Allah against them) falls into one of two categories: Either the supplicant is excessive in their supplication, believing in oppression based on a false illusion and conjecture, in which case they commit a sin. Or, they are excused in their judgment that the person has wronged them, and their error is forgiven.

Originally, the supplication of one who invokes Allah against someone who has not wronged them is not answered, but sometimes it might be. As Ibn Taymiyyah mentioned, some people may invoke Allah against others with a forbidden supplication, and it might be answered. The supplicant deserves punishment for this if their sins are not removed by repentance or good deeds. This could lead to the removal of the sweetness of faith, or the removal of the عمل الإيمان (practice/fruit of faith) (making them a transgressor), or the removal of the أصل الإيمان (root/essence of faith) (making them a disbeliever or a hypocrite).

According to al-Khadimi al-Hanafi, if the person cursed deserves the supplication, it will affect them; otherwise, the supplication returns to the supplicant. The apparent meaning of some texts indicates that a supplication of oppression might be answered even for those who do not deserve it, like the story of Bal'am with Moses (peace be upon him).

As for the saying "حسبي الله عليك" (Hasbi Allahu 'alayk - Allah is sufficient for me against you), it is not a curse. Rather, it is seeking Allah's help, relying on Him, and trusting in Him to protect the oppressed from the oppressor's injustice. It is a safeguard for every fearful person.