This issue usually arises when a customer has just ported in from a different provider. Each Skinny SIM card is provisioned to have an assigned mobile number that starts with 0204.
In some cases, the number brought over does not update the device and therefore sending out text messages using the assigned 0204 number. Rest assured, there's nothing wrong with your mobile number. To stop this issue from happening again, follow the simple procedures below!
Check if the sent messages are 'iMessages' (blue) or text messages (green).
If the message is blue - go into settings and turn iMessage on and off. This allows your Message application to refresh and receive update information.
Step 1:
Go to Settings
Step 2:
Select Phone
Step 3:
Select My Number
Step 4:
If you see a number that starts with +64204, remove and replace this number with your own number by adding +64 and then your own mobile number.
For example, if your mobile number is 021333444, then you can replace the whole number as +6421333444.
Step 5:
Restart the phone after this process and try testing