You can only upgrade to a new contract or convert to PAYG at the end of a contract (to avoid charges). If you upgrade then immediately switch to PAYG you will be charged the full amount of the contract too.
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)