How can one deal with the effects of psychological suffering and harassment in childhood, overcome the past, forgive the mother and uncle, and achieve success in life after academic failure?

What has been mentioned about your uncle contradicts religion, ethics, and sound human nature. The sadness and unhappiness you feel may be a result of your mother's negligence, or of disobeying Allah, or it could be a trial to elevate your ranks. We advise you to repent to Allah, draw closer to Him through dhikr (remembrance of Allah), reciting the Qur'an, and supererogatory acts of worship. Forgive your mother and seek forgiveness for her. Forgive your uncle if he repents; otherwise, encourage him to repent and refuse to return to the haram (forbidden) state that existed before.