That’s weird.  DOes it not even show a red dot on your phone app icon?

Just wondering if you had cellular data on? Someone mentioned that voicemail notification need that to be on.

I do have cellular data on

There is no red dot on my wife's voicemail icon in the phone app either.

Could be an apple update thing? 

My iPhone voicemail notification was still working as normal (red dot). I am running the latest iOS btw. I recommend you try to reset network settings first. If that doesn't help, you could try "reset all settings". 

My voicemail notifications don’t work either. I have the latest update on my iPhone 12, data is on, notifications are set to persistent and I have also reset my Network Settings, still no luck. I use to use “Visual Voicemail” but since Koodo increased the price I removed that addon and I now don’t receive any red dot on the voicemail mail icon when I have a new voicemail. I have to call in to find out if someone left a message if I didn’t answer their call.

Is Focus/Do Not Disturb enabled on your iPhone?

When this is enabled, this can hide notification badges.

To check, go to Settings > Focus > Do Not Disturb > Options > Hide Notification Badges - you can toggle this  on or off.

Focus/Do Not Disturb wasn’t activated on my phone.

Did you recently port out to Koodo?

.

Me, too.  Same: I just switched phones and service. Now own an iPhone  SE.  Apple Support says my settings are all OK.  I get an initial sound when a voicemail is left on my phone and I hear that if I’m in the same room.  There is a notification that there was a Recent Call, but there is no notification that there is a voicemail waiting to be heard.

Same issue here. I found that by restarting my iPhone, the voicemail badge appears and then disappears a couple of seconds later. Looks like we’ll have to wait for another iOS update for this to get fixed. Getting rid of the gigantic red dot (recent calls badge) on your phone icon requires a restart, if applicable.

I have the same problem. No notification alert, no badge to indicate that I have voicemail. I have done all the recommended solutions, but hasn’t resolved the problem. 

Just wondered if you reset "all settings" in the iPhone yet?

No, haven’t done so, as I didn’t want iPhone go back to factory settings.

No, reset all settings isn't a factory setting reset. It just simply reset all parameters of the settings to its default. Your data is still there. 

This might help https://support.apple.com/en-ca/guide/iphone/iphea1c2fe48/ios

I spoke to Koodo tech and I did “reset all settings” but it didn’t solve the problem. He has escalated it to a senior tech, so will see if they are able to come up with a solution.

Callback from senior tech said it’s a known issue with latest IOS update, and Koodo has reported it to Apple. Hopefully, next update will take care of it.