Is the fast of a person who did not made up missed fast days of the previous Ramadan accepted?

Yes, it is accepted by the will of Allah. However, after the current Ramadan, he must make up any delayed missed fast days of the previous Ramadan and feed a poor person for every fast day he delayed making up without an excuse. When there is an excuse, it suffices to make up the missed fast days.
Allah Almighty knows best.