Voicemail blocked?

After I upgraded from iPhone5 to iPhone SE, a friend who calls from Canada can no longer leave voicemail messages. He gets a message like "We're sorry. But the number you have called has calling restrictions that prevent the completion of this call." I get lots of voicemails from other callers, so I know it works. I don't have any other Canadian callers so I don't know for sure if that is the issue. I do not have an international calling plan, but there doesn't seem to be any restriction on receiving Canadian calls.
Is there any way to clear this up?
Thanks,
Owen
Is there any way to clear this up?
Thanks,
Owen