Having had 02 broadband for almost a year now and taken up the pay as you go mobile phone service a little while after I would warn any prospective new customers to be very wary of them. They may come out well on Which surveys (and in terms of technical support I wouldn't challenge that) but their systems are heavily automated and rigid and leave a lot to be desired so experience of their appaling billing and "custom service" (sic) teams are almost a ceratinty.
My experineces have included regular and contradictory information and responses. A total inability to deal with queries by email. Overcharging by not discounting broadband as they are unable to cope with pac porting across an old mobile number while maintaining the relationship with the broadband account. If you dare dispute a charge they are very poor at dealing with any query and then will suspend you without notice. I receive notification some hours by text after I had been suspended for disputing an overcharge and almost 12 hours by email after I had already been suspended ( excuse me how was I supposed to read the email when I had no service ). No warning in advance of any risk of being suspended they just took unilateral action.It takes 24 hours to reinstate an account and whats more they will charge you £10 for the pleasure without even informing you thats their intention.
They are truly abyssmal and I will be completing my contract and moving to a more reputable and professional organisation at the first available opportunty.
Judging by other comments I have read here clearly I am not the first to suffer at their hands.
Get your act together Which!