How do I turn on voicemail notification

That is the same as Phone notifications. If your iPhone is ringing, then you should also receive a notification if you receive a voicemail. You can also go into Settings>Sounds & Haptics and make sure there is a sound listed for New Voicemail.

Britliff Said:

"How do I turn on voicemail notification please"

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Contact you Carrier:

If you are not getting notifications as soon as they are left, but rather are getting them days behind schedule, then contact you carrier. They'll know the fix. It's happened to me, and its no more than the SIM card needing to be worked on.