Why does my Message show my old SIM number how can I change it?

If your message app is displaying your old SIM number, it might be due to your device not updating the information after changing SIM cards or phone numbers. To fix this, you can go into your device's settings, usually under "Phone" or "Messages," and update your contact information. Additionally, restarting your device may help refresh the settings. If the issue persists, consider contacting your mobile carrier for further assistance.