Obviously O2 don't like you very much then!
If you look at some the threads on moneysupermarket, there are plenty of people who are offered things like 500 mins and 500 texts/month for £20!
I would also demand a Nokia N80 for free too - damn fine phone. Maybe sweeten the deal for O2 and say you'll take an 18 month contract.
If your current monthly spend is less than £30 then all bets are off.
W.