Voicemail Set Up Issues

I recently changed wireless providers and upgraded to the new iPhone 11 Pro Max from an iPhone 6s. Everything got transferred over including undeleted voicemails, but it says my voicemail isn’t set up when someone calls. I can’t update my voicemail greeting and don’t see any other voicemail set up button. Is the an apple issue or a provider issue? Plz help. Thx.