The Prophetic solution to people who are harmed in private:
Abu Hurayra said... A man came and said, "Messenger of Allah, I have a neighbor who harms me." The Prophet ﷺ said, "Go and place all your belongings in the road." So he did that and all the people gathered around him and said, "What is the matter?" He said, "I have a neighbor who harms me so the Prophet ﷺ told me to place all my belongings in the road. The people began saying about this neighbor, "O Allah curse him! O Allah punish him!" Word reached the neighbor, so he came to him and said, "Return home and by Allah, I will never harm you again."*
In another narration, the Prophet ﷺ said, "Go and place your belongings on the road and whoever passes you will curse him."
In another narration, the man returned to the Prophet ﷺ and he ﷺ asked, "What did the people say?" The man said, "They all invoked lan'a upon him." The Prophet ﷺ said, "Allah's curse is above their curse. Return home for now you are safe."
In another narration, the neighbor himself came to the Prophet ﷺ saying that the man had placed his belongings in the road and was telling people about what happened between them privately. The Prophet ﷺ said, "And what did the people say?" He said, "They are all cursing me." The Prophet ﷺ said, "And Allah had cursed you before the people did." Then the man swore never to abuse his neighbor again.
In Bayhaqi's narration, the man had complained three times to the Prophet ﷺ, who advised him to be patient. Then on the fourth time, he used the public.
The lesson here. Certain things are not necessarily crimes. Other things are crimes that can't be prosecuted because there's no evidence or witnesses. So how do can we stop such harm? The Prophet ﷺ taught this man to invoke public ire against the person, and that will stop him. If taqwa doesn't stop a person, the law will. If the law can't, then public embarassment will.
*Narrated by Bukhari in his Adab + Abu Dawud, Ibn Abu Shayba, Bayhaqi, Haakim.
عن أبى هريرة قال: قال رجل: يا رسول الله ، إن لي جارا يؤذينى! فقال: "انطلق فأخرج متاعك إلى الطريق". فانطلق فأخرج متاعه؛ فاجتمع الناس عليه فقالوا: ما شأنك؟!! قال: لي جار يؤذينى، فذكرت للنبي -صلى الله عليه وسلم- ،فقال: "انطلق فأخرج متاعك إلى الطريق". فجعلوا يقولون: اللهم العنه! اللهم اخزه!. فبلغه فأتاه فقال: ارجع إلى منزلك، فوالله لا أؤذيك.