There's confusion regarding sending text messages in Mexico, as the recipient sees a different number than the one you sent it from. This happens due to a specific regulation in Mexico for mobile text messages.
In Mexico, AT&T is the only mobile company that allows texts to be sent from a regular phone number. These messages are primarily intended for person-to-person, or P2P, conversations. According to the rules, if more than nine texts are sent from the same number in less than two minutes, the system automatically changes the 'Sender ID' - the number from which the message appears to be sent. This is done to comply with Mexico's regulations.
Therefore, if your messages are appearing from a different number, it's due to this regulation being applied. To avoid this, please vote here so we can support shortcode.