I'm a bit confused though, anyone nominated by their CFA for FA appointments should automatically be set up on MOAS. And they wouldn't take you off a game off the back of just one missed call. I'm not even sure how they would appoint you if you aren't on MOAS.
Sounds to me like you were appointed on MOAS and for whatever reason didn't get the email. Perhaps you haven't confirmed your email address, or it went to junk, or an IT gremlin (not uncommon with FA IT systems) has kicked in. But you need to contact your RDO otherwise the next FA appointment will likely go the same route.