TXT message still the Id Number

Two things @Anthony Nicholls.

Firstly, this can happen if you used your handset with your new iD SIM card BEFORE your number was ported from EE to iD.
If you’ve got an iPhone, try turning OFF iMessage so text messages are sent using SMS instead - for Android, the quick fix is to turn OFF “Chat features” in the Messages app.

Secondly, bit of a grey area, but there’s a section in iD Mobile’s terms & conditions stating: 

Hi @Anthony Nicholls 

Are you on an iPhone or an Android?

If iPhone please try the following;

Tap Settings > Phone > My Number and confirm that it is correct.

If not please reset network settings, reboot and test.

If Android;

1) Open Messages, go to Settings (top right, Message Settings), open "Chat Features" or "RCS Chats", verify if this is the correct number or not.

2) If it shows the incorrect one, then head to: https://messages.google.com/disable-chat and you should be able to unregister the number. Once done, turn off the Chat Features/RCS and the phone. Wait a few minutes and turn the device back on and re-enable Chat Features/RCS it should let you re-register/update to the correct number.

Alternatively, you can turn Chat Features/RCS off and test SMS after this.

Tom