I believe if you ported your phone number over then your phone will show the device phone number as the original phone number, not your current correct number. Mine does this. When i open contacts and click on my picture at top of page it shows me my details. It shows "This phone 1" and a number i do not recognise. If i go into settings and then click about phone it shows the same number that i do not recognise so i believe this was the number originally allocated to my phone when i bought it.
I have searched for a solution to this for ages but i do not think it is something you can change, all you can do is go into your contacts and edit your details and add in your mobile number.