Transfer Number for Giff Gaff to O2

[MostlyCloudy]

I am transfering my phone number from Giff Gaff to O2.

I have no signal on my old Giff Gaff sim, therefore I believe this number is now 'dead' at Giff Gaff. I have recieved an email from O2 saying my number is the one I want not the number O2 gave me. But the number has not changed on the device despite turning off/on again several times. 

How long does this action to transfer take? 

[MI5]

@MostlyCloudy 

If you have an iPhone, go to Settings >Phone >My number.

Edit to your number, save it, then reboot phone.

[madasaf1sh]

@MostlyCloudy 

You may need to physically need to change the number on the device, this can be done through the Menu's Settings and then Sim Card Options.. for Android

For Apple 

1. Turn OFF iMessage (Settings > Messages).
2. Turn your phone OFF for at least 10 minutes.
3. Turn your phone ON and tap Settings > Phone > My Number and confirm that it is correct. 
   If it’s not correct, please enter the correct number.
4. Turn iMessage back to ON (Settings > Messages).
5. Finally, go to Settings > Messages > Send & Receive and see if the correct number is displayed under “Start new conversations from:”. 

If that fails, try doing a Network Reset as follows (applies to iOS 15+):

Settings > General > Transfer or Reset iPhone > Reset > Reset Network Settings

[RafaC]

Hey @MostlyCloudy, were you able to sort it out?