@aleeza It's too late in the day to call. O2's customer service is not 24/7. You need to call in the morning.
Call 202 from your mobile or 0800 032 1402 from any phone or numbers in this link: Guide: Coronavirus Community Help and Support
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.