Sim Card Number change

[Cameron24]

I recently got a new contract for the S21 and i gave them a PAC code to changeover my old number. When i recieved the phone it came with a sim with a new number. i used the new number for a couple of days till it changed over, now its not letting me use the new sim. Would my old number be on a completely different sim that O2 send me or do they replace the number on the new sim that i recieved with the phone? 

[MI5]

@Cameron24 

Your number should be replaced on the new sim.

If it's no longer working, you need to contact O2.
All numbers are in this guide Guide: Coronavirus Community Help and Support 
When you call, you will be asked for 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.
You can also try saying "Upgrade" or "Fraud" to be connected to an advisor.
8.00am is the best time to call if you can.