Must the bleeding days, which amounted to 70 days, be made up from a pregnancy with an empty gestational sac, knowing that I fasted and prayed throughout the month of Ramadan?

The blood resulting from a miscarriage is considered Istihadah (definition) (irregular vaginal bleeding), except for what coincides with the time of the menstrual period, which is then considered Hayd (menstruation). Accordingly, you are not required to make up the days you fasted, except for those days that coincided with your regular menstrual period, which must be made up.