Your iphone might switch to Apple Live Voicemail with recent iOS update. You could choose to use it or turn it off. Here is more information about it

Hmm. Unfortunately switching off Apple Live Voicemail did not work. Thanks.

That was strange. When people call you did it ring on your device? And if they reached voicemail ,what voicemail message did they hear? Was it normal Koodo voicemail prompt or something else?

Hi Dinh. Even though I updated my OS three days ago, I couldn’t retrieve messages prior, nor yesterday.  Things have sorted themselves out. I suspect it was turning off Apple Live Voicemail and waiting 12 hours that did it. I always could hear when people called, but their unheard messages are now gone. I can now retrieve 3 test voicemails from today. BTW, those people could hear my VM prompt, not Koodo’s.

Thank you, Dinh, for trying to get to the bottom of this with me. All good now!