Recover voice mail from iCloud backups

i recently got an iPhone x and found that my voicemails did not transfer over. I backup to iCloud only. I downloaded iExplorer to see if i could recover my old voicemails but it seems to only recover from iTunes backups, not iCloud. Is there anyway i can search through iCloud backups for voicemails? I'd like to go back even further in history than my last phone, if that's even possible. How long does apple keep back ups?