O2

I've done a stupid thing. After getting a new iPhone I listed my old one on FB marketplace.....but I forgot to unlock it first. I am not sure what to do as the phone has been reset to factory settings. I went to 02 and listed the IME number but this ...

Hi I just upgraded my phone from iPhone XS to 13 Max Pro. Will changing the SIM mean that I lose my number? I want to keep my existing number so not sure what to do. Sorry. I'm old.