Erase temp number in Apple id

[Nottslad]

Hi everyone, I hope someone can help please?
I've just ported my number over from ee but I had been using the temporary number that came with the SIM card which was linked to my apple I'd, messenger etc. Now my old number has been ported over the temporary number is still the main number and can't be erased as I can't access the number. 
I've tried changing the apple I'd password but no joy and my old number can't be activated.
Can anyone shed any light on this before I ring C/S in the morning?
Many thanks in advance for your help.
Regards
NL

[MI5]

@Nottslad 

You can try resetting your network settings.

[Nottslad]

HI5, thanks for taking the time to reply.

Being a bit of a newbie, I have a iPhone 7 plus, can you give me a pointer how to start please?

[MI5]

@Nottslad 

If you're using iOS15 or later, tap Settings > General > Transfer or Reset [Device] > Reset > Reset Network Settings. If you're using iOS14 or earlier, tap Settings > General > Reset > Reset Network Settings.

[Nottslad]

Hi MI5.

Yes it's 15.7 I think.

Just before I do when I press reset do the settings come back or do I have to get them sent to me some how?

Sorry for all the dumb questions, I appreciate your help.

[MI5]

@Nottslad 

The settings will reset themselves but you will lose any saved wifi passwords.

[Nottslad]

Thanks for your advice but no joy. I'll ring in the morning.
Thanks for your help

[MI5 · Accepted solution]

@Nottslad 

You'll need O2 to send you a new sim.

Once it arrives you need to do a sim swap Guide: Sim Swap: a mini guide 2017 update 

[StuartR1]

I've just ported from EE and everything worked after the porting was complete to 02 you can manually change the number on iPhones @ Settings > Phone > My Number which may work if not as stated above getting a new sim card will work.