Really pissed off with O2!

Called up O2 last night to do my O2 Select upgrade (being able to do it at 12 months rather than 18) only to be told that the terms and conditions had been changed and that I now no longer qualified for an upgrade at 12 months but had to wait until 15 months instead. Needless to say I was less than impressed with this news especially as I was told last December that when I upgraded I would still qualify for a 12 month upgrade next time. Have written a two page snotogram to O2 today to express my disgust at the way the terms have been changed to my disadvantage.