It will continue as a rolling 30 day contract.
If you want to leave you need to call CS on 202 and let them know.
You will also need a PAC to port your number to another network.
http://community.o2.co.uk/t5/Pay-Monthly-and-Pay-Go/Cancelling-Your-Contract-A-Guide/m-p/566774/high...
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)