Delayed/Missing Voicemail

For quite some time now I've seen voicemails seemingly randomly come through late on my phone - 1 hour, several days, and even today heard from someone who left messages I never received. Other times, the messages are received in minutes. In these many months I've of course powered my phone off/on, ensured it's updated, etc. Yet the problem remains. It is not a problem on any of the other iphones in our family plan with our carrier. Anyone able to help troubleshoot?