If it is not yet billed, on the right hand side of the my o2 main page(on a computer), about a third the way down, there is a section called "what I've used"
This gives you a breakdown of the unbilled amounts by clicking on the relevant sub section.
On the my o2 phone app if you click on the section called recent charges and that also gives a breakdown of the unbilled usage.
If it is already billed, visit the my o2 page on a computer and under the main bill amount there is a section to view a full breakdown of the bill.
If either of these are not working I strongly suggest calling customer services on 202 free from your o2 phone and select "billing and payment" and then "a problem with my bill"
Hope you get this sorted, let us know how you get on.