Hey there lenore101,
Thanks for reaching out to the Apple Support Communities.
To get started, since Visual Voicemail is a feature that is provided by your carrier, have you had a chance to reach out to them to confirm that there are no issues on their side?
If you have reached out to your carrier, and no issues were located on their end, we'd recommend testing the issue by checking new voicemails that are received while connected to Wi-Fi if possible.
If you've noticed that the transcription for voicemails don't appear after 24 hours from receiving the voicemail, try using dictation in another app, then check for the transcription once again. For help with using dictation in another app, check out this link here: Use Dictation on your iPhone, iPad, or iPod touch - Apple Support
If the issue persists after the steps above, we'd recommend reaching out to Apple Support directly from this link here: Get Support - Apple
Take care!