Is the repentance of a person accepted who was cursed by an elderly man after he wronged him, and then he gave charity on his behalf, but still feels fear and anxiety about not being successful?

You are not to blame, dear brother. You apologized to this person, and he should have accepted your apology. You have done what was required of you, and nothing further is incumbent upon you. By virtue of Allah Almighty's justice, his supplication will not be answered. Therefore, have a good opinion of Allah, and do not preoccupy yourself with thinking about this matter.