Lufus, I can understand your frustration with the provider, but this is NOT O2 specific, in your case yes it is, but you will find similar head banging situations with any of the other providers. I certainly have done this and what ever provider you have a problem with, one thing is for sure, you will pull the short straw.
I am currently tossed between O2 and Vodafone. I am on PAYG but need data plan, as iPhone is very much web orientated. O2 has bolt-on for £10/month for PAYG, but reception is very bad to No Service where I work, Vodafone has better coverage, but their Flexi pack of £7.50/month is only for contract, not PAYG, which have to pay 50p/day for web access. I have moved my current number from T-Mobile to Vodafone because of the signal problem, so T-Mobile is also out of question. I had it twice now that school tried to contact me on my mobile, because of an accident and an illness of my son and I got that message 2 hours later as I was back in signal range and that in the Midlands. Hence I really need a 100% signal coverage, which so far only Vodafone supplies.