Alerts for blocked voicemails?

I called t mobile and that was fun.  Is it possible to either get an alert for blocked number voicemails (I got a blocked voicemail that I needed and had I seen a badge (iPhone 11) it would have solved a big problem.  
 

the other thing which people have been talking about for years is not allowing voicemails from blocked numbers 

theres a long code people have that I think do it and there’s a *67## or something but I think you have to have a number for the message to go.   
 

the people answering assumed people knew what they were talking about so I was lost.  Can anyone help me dumbed down?  T-Mobile reps are clueless 

gracias