You need to contact O2.
All numbers are in this guide Guide: Coronavirus Community Help and Support
When you call, you will be asked for 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.
You can also try saying "Upgrade" or "Fraud" to be connected to an advisor.
8.00am is the best time to call if you can.
Check with your bank though as the transaction may only be pending, in which case, O2 won't claim it and it will return to your bank account in a few days.
Track usage, upgrade and get support with the My O2 appDownload My O2