It would have been for an even period of 12, 18 or 24 months anyway.
You need to call O2 to find out why but it might just be a glitch
https://www.o2.co.uk/contactus
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)