Log in with each accounts details to your MyO2
http://www.o2.co.uk/myo2Go to "view latest bill" then "view previous bills"
Note, unless you have merged all your accounts they will have different log in details.
If you don't know the log in, call customer service on 202 and they will reset the passwords for you.
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)