Arad, an Air Force officer was missing in action since 1986. According to this Wikipedia page there were numerous efforts by the Israeli government to negotiate his release, or information about him, but they all failed. His family hadn't had any information until 2016:
In February 2016, a Lebanese man, Moufid Kuntar, claimed in court that Arad had been tortured to death while being interrogated in 1988 and was buried in a forest near Mount Lebanon. Kuntar was a commander of the Syrian Social Nationalist Party and claimed that the group captured Arad after he ejected. Kuntar was charged with spying for Israel's intelligence services, but claimed that he provided Israel with false information of Arad's fate until his court appearance
To me it seems highly unusual that a hostage has no access to any humanitarian organization and it is not even clear (for decades) whether he's alive or dead. According to the Wikipedia page, there were numerous efforts by the Israeli government to try to retrieve him, but I hadn't seen any notable efforts by the UN or other humanitarian organizations mentioned. Were there any?