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

Yes, it is accepted, by the will of God. However, after the current Ramadan, it is necessary to make up any delayed missed fast days of the previous Ramadan, and feed a poor person for every fast day one has delayed to make up without an excuse. When there is an excuse, it suffices to make up the missed fast days.

And God Almighty knows best.