3rd party phone service stop working beginning of June 2024

Have been very happy with our T-Mobile phones and internet,  until now.
My wife has been working from home on a land- line phone (connected to our t mobile black tower) for the past 2+ years with no issues.  About a month ago her "work" phone stopped working.  There is a dial tone, but she is unable to call out or receive calls. Her work IT folks think T-Mobile is blocking 3rd party providers. 
T mobile Tech Supports fix was to try the new white tower. It didn't solve the problem. 
I see others talking about the SIP/ALG, and that it should be disabled, but T-Mobile support has been of no help.
Anyone else experiencing this issue?