1. Open Calendar app
2. Tap tripple dots in upper right > Calendars
3. Tap Cancel if asked about Samsung account
4. UN-CHECK the boxes by "My calendars" and "My task"
5. Tap the back arrow in the upper left
6. Now if your calendar still displays the expected appointments your calendar appointments are saved in your Exchange account and you are set up correctly.
7. If not, follow the steps below.
7.1. Turn back on "My calendars" and "My task" and turn off the calendar for your email address.
7.2. Then write down those appointments.
7.3. Then turn off "My calendars" and "My task" and turn on the calendar for your email address.
7.4. Then re-create the appointments.