There have been a few problems with this recently.
Submit the form again https://www.o2.co.uk/help/phones-sims-and-devices/how-to-keep-your-mobile-number but nothing will happen over the weekend.
You should get a text confirming a changeover date if the request is received successfully.
If not, call O2 to chase it up Guide: Coronavirus Community Help and Support
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.