What should I do about making up days I missed fasting in the past, without knowing their exact number, especially since I previously paid a fidyah for them?

A Muslim must learn the necessary Sharia rulings, including the rulings on fasting. Paying money instead of feeding is not permissible for those who break their fast in Ramadan due to an excuse, such as the elderly or those with a chronic illness. Rather, what is obligatory for them is to feed one poor person for each day. Any money paid is considered charity. You must make up the days you missed, either by certain calculation or by strong presumption. Consecutive making up is not required, and you must begin by making up the Ramadan of the previous year before the next Ramadan begins. The preponderant opinion is that what is obligatory is fasting only, unless you are able to combine it with feeding, which is good. If breaking the fast was without a legitimate Sharia excuse, there is no making up; rather, it requires repentance, seeking forgiveness, and compensation through supererogatory fasting and good deeds.