See if anyone disagrees with me or has a different idea.
I believe you have two options, see if you can get T-Mobile reception by moving your device closer to a window, or else use wifi if you have that option. If the first case, if you get reception, it may be good enough to at least know you get a call and to receive email and messages.
The reason I say that is I have sort of the same experience sometimes. In my office my device can't see T-Mobile sometimes and it connects to AT&T for emergency calls. Reception will mysteriously strengthen and my device will connect again. When it is worse, I put my device on the windowsill.
In your case I think the same thing is happening, except Telcel instead of AT&T.
If there is a way to manually select the network, I don't know how that would help if the device can't see the network to begin with.
The Mexican networks are notorious for allowing signal to bleed over the border.
Is there office WiFi that you can use? If so, put your phone in airplane mode and turn WiFi back on. You might also be able to lock your phone on a band that's not used across the border.
I've owned phones that allowed me to disable voice and text roaming. I don't know of any current phones with that feature. Manual network selection may help.
Hey there! What kind of phone are you using? You should be able to manually select the T-Mobile network and it will not switch to Telcel on its own
As many have mentioned, a manual network selection would definitely help out. If you'd like specific steps on how to do that with your device, please let us know what model phone you're using.