Log into your MyO2
http://www.o2.co.uk/myo2 and change your tariff to Classic PAYG, or give customer service a call on 4445.
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)