Why doesn't calendar app on my Galaxy Note 3 sync with my work Exchange Server?

[AC Question]

Only some appointments show up on any of the calendar apps I download. I only use the calendar for work so it is supposed to sync with our Exchange Server. The app that came with the phone disappeared so I've had to download calendar apps from Google Play but none of them seem to work. I have turned the phone off, taken out the battery and restarted the phone and still nothing. Help!!!