iphone SE visual voicemail not working

I had the same problem.  I upgraded the phone on one line and then moved the old phone to one of my other lines.  Xfinity Mobile needs to update stuff on thier end to reflect the change.  Log into your account, scroll down and click the link for Xfinity Assistant and ask the bot to connect to an agent.  Explain to the agent you moved your sim from an old phone to a new phone and visual voicemail is not working.  You will need to provide the IMEI number.  Make sure they understand the sim moved to a new phone and they need to update their side or they will run you through the normal troubleshooting script, which will not work.  

I've chatted on tier 1 level and got a CR ticket#,  called into tier 2 and spent about 2 hours,  the person there wasn't any better than the tier 1 agent,  except she had access to ask others in tier 2,  (who she said were smarter than her) she spoke with several others and none could figure it out,  then she messaged someone in tier 3 who said that if I can access voicemail than it's built and it's set to apple voicemail,  otherwise wouldn't work at all;  nothing they can do on their end,  this is an iphone app and I need to contact iphone.  Complete waste of time and very frustrating.    I decided to get a 3rd party app for now that's free called YouMail.   I'd rather have a visual voicemail through the provider - xfinity mobile but it doesn't look like they can fix it

Try again! You need a tier 2 specialist that can modify the back end voicemail settings from Android to Apple iOS.