My Mobile No has vanished!

Hi everyone, I hope you can help me.  I purchased a Smarty SIM some time ago and requested that I keep my old No instead of the SIM's number.  That has been fine until I decided to change my Iphone to a Samsung.  Although I can receive messages and phone call okay, when I send texts and make phone calls the original number of the SIM shows up instead of my own number.  Is there anything I can do to correct this, or do I have to start all over again with a new SIM? 

I hope someone can help solve this problem. By the way, I can see that my correct number appears here.  Thanks for listening.