55p per min is just the access charge.
There is the service charge to add to that.
You need to dial +44 845
https://www.o2.co.uk/help/account-and-billing/other-numbers-and-charges
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)