Hey @albertmusco I hope you are doing well!
I just want to make sure I am understanding, you used to have a prepaid plan and now have a regular plan with the same number as the prepaid and you are unable to set up the voicemail?
Have you tried pressing the number 1 for three seconds, that calls your voicemail and it should indicate you how to set it up.
I will also leave here a link to one of our library articles regarding the usage of voicemail.
Let us know if you have any further questions!