First, try to deactivate and reactivate iMessage on your phone. On your phone, go to Settings > Messages > iMessage and turn it off and on.
If your iMessages are still being sent from your temporary number, check if your settings are updated. Go to Settings > Messages > Send & Receive and make sure the correct mobile number is displayed under the 'START NEW CONVERSATIONS FROM' section.
You can also try to reset your network settings on your iPhone. Go to Settings > General > Reset > Reset Network Settings.
Please note that you may be charged by Apple for the activation requests sent to Apple Servers each time you activate/reactivate the iMessage function. For more details on iMessage settings, you can check out the dedicated Apple Support Platform here!