Is what happened to this person—injustice and mockery—proof that his repentance has not been accepted, and what should he do to remove the affliction?

If a person repents with sincere repentance that fulfills its conditions, then Allah Almighty accepts his repentance and overlooks his sins. The affliction that befalls him after repentance may be due to other sins he has not repented from, or it may be a test from Allah to raise his rank and expiate his misdeeds. Therefore, he must be patient and seek help from Allah. He should also remind those who mock him that their action is impermissible and exposes them to Allah's wrath and punishment, and he should seek help from those who can deter them and repel their aggression.