Answer
(Fatwa: 337/337/M=1433)
Masah is valid either on leather socks or socks which fulfil the conditions that make the masah on socks lawful, i.e. the sock is so thick that it does not split by walking three miles and sticks to the feet without fastening. Masah is not lawful on the prevalent cotton or nylon socks. If you did masah on cotton or nylon socks then masah was not correct and salah offered with that wudhu was not valid. You should reoffer those salahs again which you offered with that wudhu.
Allah (Subhana Wa Ta’ala) knows Best
Darul Ifta,
Darul Uloom Deoband