Have you checked your allowance on myo2 to see if you have any left this bill cycle? If you have no data left in your allowance it makes no difference if you paid your bill as the date it resets is different from the date you pay the bill.
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)