Do you have good coverage in the area you are experiencing this?

iPhone 11 shows 3/4 bars inside home and 4/4 bars outside.  This has occurred at random places all over Kitchener. We drove around Kitchener-Waterloo to test this. I believe a town like Kitchener Ontario has good coverage. I am new prepaid customer. This is not a port. I got new SIMs from Amazon and activated it online. There was no problem when we were in Toronto for the past three weeks. We moved to Kitchener this week and the issue started. We have two SIMs, both SIMs have this random calls going to voicemail problem. This problem started when we moved from Toronto to Kitchener.

Try resetting network setting of the iPhone and see if it still persists?

If you know other people in your area with either Telus or Koodo (or even Bell), ask them how their reception is. Koodo prepaid doesn’t give any less priority to their service than any of the others, so if other people have great reception, you know it must be something else...

Thanks, but I tried reset already. Now I am thinking if it has something to do with us switching cities. Toronto → Kitchener. Maybe the cell is caching our service in Toronto towers and thinking we are not in range ? I am not a cell service expert though.

Have you tried to reactivate your voicemail? I would suggest disabling it and setting it up again to see whether it will fix the problem.

You can follow the instructions here. https://www.koodomobile.com/en/help/voicemail

No, it should definitely connect to the nearest tower no matter where you are in Canada. Check the spam filter on your phone. I set mine to block all suspicious calls. I also get random voicemails and the phone never rings, but those are invariably spam calls in my case. Just trying to think out loud here… it is strange that you receive some calls and not others.