How can one get rid of addiction to pornographic websites and masturbation given the inability to marry, and is castration permissible to eliminate this problem?

Islam has forbidden everything that causes harm. Watching pornography and what follows it, such as masturbation, is unlawful and reprehensible. It is among the causes of spiritual diseases and hardening of hearts, in addition to leading to many physical ailments and being a cause for falling into forbidden acts. Allah has commanded the believers to lower their gaze and guard their private parts.

A Muslim must sincerely repent to Allah, stay away from everything that incites lust and from bad company, and be conscious of Allah's watchful eye. He should fast, for it is a shield, and strive against his lower self, and perform many supererogatory prayers and night vigils, and engage in worship, remembrance of Allah, supplication, and seeking forgiveness. He should also remember death, Paradise, and Hellfire, and stay away from sins and transgressions, and be patient and seek help from Allah.