Bill

[Jess96]

I have recently got back from being abroad, to find out I have a massive bill this month and next month. I was using WiFi calling, so i am not happy to pay what you are charging me 

[MI5 · Accepted solution]

@Jess96 

Wifi calling just uses your regular allowances so if outside of EU you will be charged at international rates. 

Guide: Roaming MegaGuide 

[Bambino]

@Jess96 You can see what the charges are here: How do I get to the 'Download Bill' page? (o2.co.uk)

If you are unhappy about what you've been charged you can speak to customer service. Call 202 from your mobile or 0344 809 0202 or 0800 032 1402 from any phone or numbers here: 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.
You can also reach O2 via social media:
Facebook (https://o2uk.co/O2CFB), Twitter (https://o2uk.co/O2CTW), or Instagram (https://o2uk.co/O2CIG)