The call you are trying to make may not be included in your allowances.
See list of special numbers here
http://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)