What is incumbent upon someone who does not remember if they broke their fast on a day in the Ramadan before last?

If one doubts the fasting of a make-up fast (qada') or an expiation (kaffara) for which fasting is obligatory, then he must fast, because the default is not fasting, and this default is not removed by doubt. And if the make-up fast was delayed without a valid excuse until the next Ramadan arrived, then in addition to making up the fast, he must feed a poor person for each day.