pay up Front for Life on o2

I have an o2 tarriff pay up front for for life. I could have chosen 50 minutes peak or 200 minutes off peak. I opted for the 200 off peak minutes, I was told a couple of years ago that I could change to 50 minutes anytime, but I could not change again, you could only change once.

I wrote to them a couple of years ago because I could not work out what they were charging me for the peak calls and texts, as I do not have itemised billing.That costs 99p per month and my bills are not usually that much anyway, because I just tend to use the free time mostly.

The bills that I have been receiving for the last few months have a tarriff shown on them, and the charges are completley different to the one I am supposed to be on. Most of them are lots more per minute. It also appears
the the peak times have changed, peak time. now starts at 7.00am Monday to Friday, my letter shows it should start at 8.00am, so I am losing an hour every day. I often made calls at this time and only realised when I started to get charges on the bill, I know I had made no chargeable calls, and it was because the time had changed. I have written to them and am getting no where they just skirt around the issue, and it is a waste of time phoning customer services because, no one seems to know about this tarriff.

I emailed them last week and thought I was getting somewhere, as they said they had passed it on to the relavent dept., but no today they have replied telling me to phone customer services. I have now asked them for the name of some one in authority that I can write to.
Has any one any other suggestions?