iPhone Voicemail Notifications not working / delayed

Hello community,

First time poster here. Dealing with an unusual issue -- google searching proves others have this issue yet no real solutions. My voicemail is essentially working fine... however the notifications are not. I will miss a call and see the notification for the missed call, however no notification that a voicemail has been left. Now, if I dial "1" on my phone, the voicemail will be there. If I manually head to visual voicemail myself on my phone, the voicemail will generate there as well, almost right away or after a few seconds. I noticed that if I don't manually check for my voicemail, it may come eventually. For example, I missed a call and did not check it manually in this instance. 54 minutes later, I received a VM notification. Suffice to say, there is no clear timeline. In the past I missed a call and didn't check my voicemail for many, many hours, and found there was one there when I checked manually. Notification never came. Clearly a troublesome problem to have, especially when your cell phone is your main work phone and this is the whole reason why you went with the most "professional" and certainly most expensive iPhone apple has to offer...

At this point, I have done all the possible fixes found online. Don't bother asking, I've done them all. Yes, my notifications are set correctly. Yes, I've toggled Siri settings on and off. Yes, I've toggled airplane mode on and off. Yes, I've reset networking settings. Etc, Etc, Etc. I've done it all. Things I've noticed: 1. Most of these fixes are for voicemail not working properly as opposed to just the notifications. 2. Performing tests after these fixes (calling from my wife's phone and leaving myself a message) would sometimes temporarily fix the problem. But not a permanent fix. It would always revert back to the same issue (this has been going on for several months at least, with loads of testing).

A chat with apple support only led to the same "fixes" I had already performed, and a suggestion to update my iOS from 13.3.1. to the newest 13.4.1. I am not foolish enough to upgrade to a new iOS that's only been out for a few hours. I asked for another solution and the only other one given was to try calling my carrier (T-Mobile) and ask them to "re-provision" my voicemail. Not sure what this means exactly, but it was explained to me as basically resetting the voicemail through the carrier. The most important thing I took from this conversation was the support team member admitted the engineers were aware of recent issues with voicemail notifications and this is happening to others.

I am not confident I will get a solution on this forum that I haven't already attempted but I also wanted to post this because I know there are others with this issue. I hope I can continue to update this as I take the next steps. Not sure if I will try calling my carrier first, or try updating my iOS first. I've been screwed on updating my iOS too soon on past devices, so I won't be doing that until I've done sufficient research.

Other factors to note:

• Running iPhone 11 Pro Max 13.3.1
• Due to the current situation in the world, the testing and experimenting has all been done at my house.
• Not sure if this matters at all, but figure everything is worth mentioning -- I am currently using something called a T-Mobile Personal CellSpot in my home. It is a device that was sent to me because I had poor cell reception in my home. With the device, I have excellent 4G LTE coverage along with excellent WiFi in my home. Not sure exactly how it works, but was described to me as "piggybacking" off the WiFi to provide better cell coverage in my home.
• I typically like to have WiFi Calling on ... but through experimentation and testing have had WiFi Calling completely off the last few weeks. While the notification problem persists, I found that turning off WiFi Calling solved an even bigger issue I was having before, where the voicemails would sometimes not even appear in visual voicemail when manually checking.

Thanks to everyone for reading this lengthy post. Here's to hoping we can figure this out.