Did you look in your phone settings? Typically it's under call settings in your dialer app. Open your phone dialer, click the 3 dot menu at top right and then go to settings. Choose voicemail (not the voicemail selection before the settings) and you should see a section with the voicemail number. If you do actually choose the voicemail menu option, it should dial your voicemail number and you will see it on screen. If it does not dial the number, then you must contact your carrier, as that means a voice mailbox was not set up for your account.
