In an email, you may end by telling the contact what you want them to do next. In a voicemail, though, ending with something like, “Call me back,” or, “If I don’t hear from you, I’ll call next week,” can discourage the person from responding.
In addition to showing active listening, you've also awoken their curiosity about what question you want to ask. Once they're back on the phone, you can confirm a date and time for your next meeting.

When we call our friends and family, we often call and hang up without leaving a voicemail -assuming the missed call will be notification enough that we want this person to call us back. Even though this is acceptable to do in our personal lives, phone call etiquette in the corporate world plays by different rules.
All sorts of funny issues can occur when your phone hasn’t had a reboot in a while. Rebooting allows your phone to clear out and fix any issues. So try switching it off for at least five minutes, then see if the problem is resolved.