You could check your blocked numbers list to confirm if Koodo’s number is in the list.

Apple Help checked all the possible issues related to the settings on the phone.  I can confirm that the Koodo number is not blocked, it is in my Contacts and is a Favourite. 

Is this the only number that goes straight to voicemail?

No, there are at least 2 other numbers, which is why I was trying to get help. Same situation: in my contacts, favourites, not blocked. 

Which phone are you using? have you turned on any “focus mode” or special mode of your device? Can you add the call back number (1-866-995-6636 ) to your contact list?

By the way, as you are here, what was the issue that you need to call Koodo? you can ask here. Someone might know the answer

All the details are in my original post and reply to Goran. 

Oh, my apologies! Was focusing on the issue of callback and mistakenly thought you wrote about the same issue.

I didn't see you mention about the iPhone model though? Was it running iOS 17? How about your signal reception in your area? Is outgoing text, calls working normally?

When you reset the phone to it's default factory settings, did you restore to the same backup? Have you tried to reset it without restoring from the backup?

I finally reached a rep who found the solution. I had the “Do not disturb “ function set to 11PM - 7AM” and although all the problems occurred outside of those hours, turning it off completely seems to have resolved the issue.