Best answer by Mohammed
I've edited your post to reduce the size of the font here as you incorrectly seemed to have typed this using the header option.
I've also moved your topic to the Coverage section for now pending confirmation of the below question.
I'm going to take a shot in the dark here and guess that you're using an iPhone if I'm correct?
This is a very common issue that's only found on iPhones and it's caused by iMessage.
When you port your number over, iMessage doesn't automatically update this in some scenarios meaning a manual update is required.
1) Try turning off iMessage (Settings > Messages)
2) Restart your phone (by pressing and holding the on/off button)
3) Tap Settings > Phone > My Number and confirm that it is correct.
4) If it is not correct, please enter the correct number
5) Turn iMessage back to On (Settings > Messages)
6) Finally, go to Settings > Messages > Send & Receive and see if the correct number is displayed under “Start new conversations from:”.
Though, if it's not an iPhone, please let us know and we'll troubleshoot further.