Hiya,
Firstly, you need to write and complain to Phones4u. They have misadvised you on the prices of connecting to the internet using your mobile phone - the £1 a day is for if you want to view the internet on your phone, not using your phone as a modem - using the phone has a modem costs alot, lot more as you have seen for yourself.
I would get in touch with Phones4u, they have misadvised on the charges - Vodafone I'm sure will be happy to help with some sort of resolution, even if its a spread payment option and to put a spend checker on the account for any future usage so it can't happen again.