You must pay the full bill that O2 generate but if you end up overpaying they will refund you.
Seems a bit silly but it's the way the billing system works and if you don't pay the requested amount you will end up with a default on your credit account.
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.
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