Sim not working

[Te8888]

My sim has stopped working

[MI5]

@Te8888 

Pop into your local O2 store with photo ID or call customer services.
You can use Skype to call if no other phone.
Guide to using Skype: Guide: A Guide to Skype 
Call 202 from any O2 mobile or 0344 809 0202, 0800 902 0217 or 0800 032 1402
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.
Say 'Upgrade', 'Lost/Stolen', or 'Fraud' if the suggestion above doesn't get you through.
Best time to call is 8 am.
You can also reach O2 via social media:
Facebook (https://o2uk.co/O2CFB), Twitter (https://o2uk.co/O2CTW), or Instagram (https://o2uk.co/O2CIG)

Guide: How can I sort out my network issues? 

Guide: Is the network down for me or everyone? 

[Dave_Gra]

in what sense? are you upto date with payments? have you tried taking out the sim and leaving it for 5 mins and putting it back in? does the phone read the sim? try giving it a clean or cleaning out the sim holder in your phone? you may need to reset your phones network settings.. if all else fails i would go to your nearest O2 store.