Locked UICC Help Needed

I have a Samsung Galaxy Note 20 that has been fully paid off. TMobile said the phone was unlocked. At that point, I ported my number over to Comcast. Once the port was successful, I tried to use the phone with the Comcast SIM only to see that there was an error. The device has a UICC lock  to Sprint that I was not aware of. I have been on the phone for days with TMobile to get the UICC lock removed but I’m not having any luck. I can’t unlock the device from my end. Settings > System Updates > UICC Unlock does not work. I see a message of “System Initializing” and then it disappears within seconds. I need help.