Are acts of obedience and repentance accepted while there remains an injustice against another that cannot be returned or absolved? And what is the classification of such an act?

This sin does not prevent the acceptance of good deeds or sound repentance if its perpetrator strives to fulfill its conditions, among which is restoring rights to their owners. If unable to do so, he must resolve to restore them in the future whenever it becomes possible, along with frequent supplication and seeking forgiveness for himself and for those whose rights are due.