Wi-Fi Calling on ASUS ROG Phone 9 Pro

I purchased this phone back in January directly from ASUS after confirming that it was compatible with T-Mobile networks. When I recieved it I was surprised to find out that Wi-Fi calling is not by default provisioned for the phone when a T-Mobile SIM card is inserted into the phone. This is what the settings menu looks like when you search for Wi-Fi calling: 

Accessing the Testing menu by dialing *#*#4636#*#* aand going to phone information brings up this menu:

Note that the slider for Wifi calling is greyed out and I am unable to put it into the ON position.

So I called T-Mobile tech support and after going through the basic troubleshooting steps I was escalated to tier 2. More troubleshooting steps but I was finally able to get them to understand that the phone has to be provisioned on their end for this to work. A ticket was opened for tier 3 support to look at within 3 business days.

During this time whatever tier 3 did to provision the phone worked as after day 3 I was able to move the slider to the on position after cycling the Mobile Radio Power from on to off, waiting 30 seconds, then off back to on. In the normal settings menu on the phone the option to turn on WiFi calling was now visible and selectable. I turned it on and it worked flawlessly. I was able to make and recieve calls over WiFi.

However after about a month of it working I updated my phone to the latest software version and for whatever reason the option for WiFi calling was no longer available and the slider in phone information from the testing menu was back to the off position. 

I have been on the phone with T-Mobile tech support 5 times now asking them to re-provision the phone, but I just cant seem to get someone who understands what needs to be done. Its extremely frustrating to have to go through hours of basic troubleshooting steps every time I call only to be told its either 'out of scope' or 'contact the manufacterer' (which I have also done who confirmed this is a T-Mobile issue). 

As I see it, all I need is for someone in tier 3 support (who dont talk directly to customers) to press whatever button they did before to provision the phone for WiFi calling again.

As far as troubleshooting goes I have done everything they have asked up to and including factory resetting the phone, twice. Has anyone had this problem with T-Mobile or have any advice on how to get ahold of someone more technologically knowledgable at customer support (i.e. tier 3)?

Thanks for reading, I know it was a bit lengthy.