Not receiving texts to transferred number

[Nutmeg]

Hi - I've moved to O2 from another network.  I've brought my old phone number with me, it works fine mostly (I receive some texts and can make and receive calls from/to my old number) however, I am not receiving texts from some of my contacts.  They are showing as 'delivered' to the sender but I am not getting them.  When I text those contacts, the text shows as being from the temporary number I had from the O2 sim before my new number was transferred. I think it may be limited to the contacts I texted from the new phone (using the new number), before the old number transferred over. Does anyone know how to fix this so I receive the texts, and so texts I send to these contacts show as being from my old number?

[MI5 · Accepted solution]

@Nutmeg 

If iPhone, Settings >Phone >My Number. Edit save and reboot.

If Android open message app >Settings >Advanced >RCS and register your correct number.