Sounds like a difficult problem not being able to call or receive messages in a timely manner!
I suspect the APN settings are not properly addressed. Want to help me with making sure your device's APN settings are set properly?
Use this link to set the APN for your Sony Xperia XZ.
Please update me and let me know what happened!
I'm having the same issues and it's getting ridiculous. I'm going back to Verizion, they're expensive, but reliable.
Sorry for hearing that you'll be considering changing carriers! Before you do so, have you had a chance to contact our customer care?
Have you had a chance to check your APN settings?
Since you have mentioned that your device is an unlocked Sony Xperia XZ. I checked your device specifications and saw that your Xperia device is able to support band 2, 4, 5 and 12. It could be possible (but highly unlikely) that the area that you are living in does not support these bands, and instead has much higher bands, like band 66 and 71.
I highly suggest that you contact the customer care team (611 from your T-Mobile device) to discuss your personal issues with your device. I wouldn't want to see you leave the T-Mobile family!
I have a MintMobile and my wife has Lycamobile(both these are MVNOs running on T-mobile network). I started seeing this issue from around Mar 2019. One phone is on LG G6 and the other one on LEECO S3. The issue is more frequent on LeEco compared to the LG phone. I tried swapping the simcards between the phones, tried switching off wifi-calling, tried toggling voLTE, but the issue keeps reappearing once in a while.