Every month my bill is a different amount. I signed up to this tarrif as I was crossing over from another about 24 months ago and since then I have noticed my bills fluctuate dramatically. My friend also had the same issue and was able to stop her tarrif when she upgraded. I have no means to upgrade right now as I have lack of funds and for the time being I don't need to. However when I changed to this tarrif I was told that it was a stuck tarriff, does anybody else get this and if so why? How do I stop it going above the set amount I signed up for??