Open the Phone app
Tap Voicemail
Check the list for the old voice message
Tap the message to play it
If it is not visible, tap Deleted Messages if available
Restore the message if the option appears
Check the Messages app if the voice message was sent there
Open the conversation
Find the audio message
Tap and hold the message if needed to save or forward it
Check iCloud backup if the message was deleted
Restore the iPhone from a backup that contains the message
Contact your carrier if voicemail was removed from the device but may still be stored on their server
Use a third-party recovery tool only if you have a trusted backup or recovery source