Is it possible to cancel a t-mobile contract with no charge?

[DavidSizer]

Hi, I recently called t-mobile to check if I could cancel my account assuming they would say no as I had an upgrade in Jan 2010. The lady at tmobile said im under no contract and can cancel anytime. I asked her to check if she was 100% and she was...i then said id phone back later to see if maybe she didnt know what she was doing, so i rang back later and again someone else at tmobile told me I could cancel my contract as it ended in Dec 2009 (my old contract). Now i've cancelled it and paid £15 to be put on Pay as you go and I have asked for a confirmation letter to be sent to my house.

My question is how come when I went onto MyTmobile website before I cancelled the contract it said I was under an 18 month contract? 24hours after it says it is cancelled..
Will I be charged for this if they find out they made a mistake?
Its rather strange, also when I rang up tmobile a month after my new upgrade to get internet put on my phone the advisor couldnt do it as she couldnt see how long my contract was eg. 18month or 24month. Im guessing the tmobile shop that gave me the upgrade maybe made an error somewhere or didnt sign me up to any contract but i have somehow just been paying monthly bills.

Im hoping to get an iphone under o2 but dont want to sign up to anyother network until im sure that tmobile will not surprise me with a huge bill

Any advice would be appreciated.

Thanks guys