Trouble changing my primary number

When I joined Smarty I ported my number from my previous network. Everything worked fine. However, the phone number shown in my Phone settings (IPhone SE) is the  original number the Smarty SIM card arrived with, and not the new number I have ported. I have tried to change this manually to my correct number, but it just won't change (more precisely will not save the change). Any suggestions of what I need to do? Thanks