@Tammy3How do you mean its trying to charge you for a bill you don't have.
Did you have a previous contract and not cancel it at the end of the minimum term?
I would suggest calling o2 on 202 from your handset or by live chat if/when available from
https://www.o2.co.uk/contactus
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This is a customer to customer forum, and there is no o2 support on here, and we do not have access to any personal or account information,
We are all customers like you and I don't work for o2,