Occasionally, this happens to me on my iPhone. Someone calls and leaves a voicemail. I can listen to the voicemail, but what I prefer to do is read it. For whatever reason, the transcription feature is not working. There is a possible fix for this issue, here is how that works.
Transcription Not Working
Sometimes, resetting the iPhone’s network settings can resolve this transcription issue. To do that, go into the Settings area and tap on General.
On the next screen, tap on “Transfer or Reset iPhone”.
In the next window, choose “Reset”.
You can reset all kinds of things in this next screen. You should select “Reset Network Settings”.
Next, you will see this window.
Tap on “Reset” and the next screen gives you a warning window.
Just tap on “Reset Network Settings” to continue.
You will have to enter your iPhones passcode and the network settings are reset. Your iPhone will restart. You will have to select your local network in the Settings area and enter your network password.
Hopefully, this reset procedure will re-enable your Transcription feature.