Look in your MyO2
http://www.o2.co.uk/myo2 and it should tell you under the full bill breakdown details but if you still can't figure it out, give CS a call.
http://www.o2.co.uk/contactusIf you have been abroad it could be O2 travel service?
I have no affiliation whatsoever with O2 or any subsidiary companies. Comments posted are entirely of my own opinion.
This is not Customer Service so we are unable to help with account specific issues.Currently using:
Pixel 7a (O2 & Lyca), One Plus 6 (Sfr), iPhone 12 Pro Max (Vodafone)