Yes you can (subject to credit check) although you will need to have both contracts running for the first month so you can transfer your number to the new contract.
Once you have obtained the new contract you will need to call customer service on 202 to switch your number and cancel the old contract.
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)