Correo de Voz Visual

Same thing with me.  I have a Samsung Galaxy S20 5G (~2.5 yrs old).  Visual Voicemail worked fine for me until 3 months ago when I had to get a new SIM card.  When I try to open the visual voicemail, I got that same message too: "Visual Voicemail detecting new Sim Card & can't connect to the network"

Every time I called for tech support, the person eventually says there's a network problem, a lot of people are reporting the same problem, and it will be fixed in a few weeks.  I call back in a few weeks because it's still happening.  3 or 4 calls with at least an hour on the phone each time.  The really weird thing is, my wife has the identical phone and her visual voicemail works fine.  She's never had a problem with it. 

Today, as I was waiting on hold for tmobile support, I was checking this string looking for a solution and tried opening visual voicemail (one more time).  Suddenly it's working fine.  

No advice to give you beyond keep trying to  open it, and try calling support once in a while.  Maybe write a nasty-gram to customer service.  Maybe they'll give you a small credit on your account.  Good luck.