o2 Issue

[t-mids]

don't know if this is in the right section but here goes...

I was called in April by a sales rep from o2 asking me if I wanted to renew my contract... They offered a good deal and I asked if the data package (internet) that came with the tarriff was unlimted use and had no fair use policy (for those that don't know this a fair use policy is when they say you can use upto a certain amount before they question you and move you to a different tarrif).... Anyway the sales rep said it is completely unlimited, no fair use policy and I could use the internet on my phone as much as I like, I accepted and last week I got a text from o2 stating that i'd breached the fair use policy, I called them up explained what the sales rep originally said (and that I had recored the sales call, which I had done) and they said they would get a manager to call me back. Are o2 legally bind to provide what they said they would and what if they don't can I take any action against them ??