Call

[Salih]

I can’t use my phone

[Bambino]

See these guides:

How can I sort out my network issues? - o2uk

Why do I have poor coverage indoors? (o2.co.uk)

Wifi and 4G Calling explained | O2

If none of that helps, download Skype: Guide: A Guide to Skype 

Call O2 free on 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 (now X) (https://o2uk.co/O2CTW), or Instagram (https://o2uk.co/O2CIG)