**** Cancel it now and shop around.
Look at it this way, he had 10 hours on the phone and unlimited texts and still spent and additional £100 on calls/extras. Its too much, and unless he's a crazy socialite, which i doubt (no offence, as people can call him and the texts are free) it should never be that.
Operators will cream their pants when someone who isnt' connected to any other networks walks into the store as a new customer and you can hold them all to ransom or just go elsewhere,
if you want to stay with O2 call them up, and say whatever the fcuk it was that made that last bill cost £130 you want it all covered in a £30 a month line rental, if they don't tell them to fcuk off.