on 03-07-2020 18:11
@KpT Might sound silly, but if the sim is working in your old phone but not in the new one, you're either not putting the sim in the right way, or the phone is faulty. Did the new phone come with a new sim? If so you could do a sim swap. https://community.o2.co.uk/t5/How-to-Guides/SIM-Swap-a-mini-guide/ba-p/1060675
If you have an O2 store nearby, call in and see if they can help. If you're not happy about going in store yet it , and it still isn't working after you've reinstalled the sim, call customer service and ask them to send you a new sim.
If you've exhausted the sim alternatives, you may have to send the phone back for a replacement.