How can I phone my voicemail?

[Julia Thomas1]

This may seem like a silly question, but I have had an iPhone for the past two years and am struggling to adjust to android! I have a notification saying 'new voicemail' but underneath it says 'voicemail number unknown'. On my voicemail settings, my voicemail number is 1, but when I call it, nothing happens. I'm really confused! I'm also confused about the voicemail forwarding settings, if anyone is able to explain everything to me that would be great. Thank you!