Can't change contact preferences in My O2

[Irrelevant_Name]

Hi

So I've just switched to O2 today, kept my number. When my new SIM arrived I signed up to My O2 with the number supplied on the SIM. However, that number is now 100% dead and deactivated as my old Three number has now transfered to my new O2 SIM. This means when I try to change my contact preferences, O2 send a code via text to the dead number and I am basically locked out. No option to verify by email that I can see which I think is pretty stupid.

I had the idea of deleting the account and starting again. Tried to delete my account in the My O2 app which appeared to work at first glance but apparently it only deletes the account stored on the device and not the My O2 account itself. So that didn't work either.

What do I do now? Is there a free helpline I need to ring somewhere or even better a web contact I can use?

[MI5]

@Irrelevant_Name 

You'll need to call customer service.
Numbers here Guide: Coronavirus Community Help and Support 
Or advice from an O2 Guru regarding a way to get through:
If you call 202, when it comes to the reason you are calling stay silent for 15 seconds and you will be taken to the keypad options.
Press 2 for Everything Else
Press 5 for More Options
Press 7 for Anything Else which will put you though to someone.
Say "Upgrade", "Lost/Stolen" or "Fraud" if you have to, to get put through to someone.

[Irrelevant_Name]

Thank for your help. However, when I logged into My O2 this morning, it seems everything has sorted itself out somehow and the dead number has been removed from My Devices completely and my actual number is now the only one listed. Security texts are now bing recieved correctly by my active number.

I will save that advice in case I need it in future though, it seems difficult to speak to an actual human at big companies these days. 

[MI5 · Accepted solution]

The system does update overnight @Irrelevant_Name 

so recent changes are often updated then.