mobile phone contract

me4_2

In 2008 I signed up to an o2 mobile phone contract, through another company, for 3 years. Within the contract I was entitled to a new phone every 12 months. I upgraded in 2009 and again in 2010, each time signing that I had received my new phones - they were sent out in the post. My contract, as I thought was due to end in Aug 2011, but I am now being told that I signed a new contract last year and that not only will my contract now run until Aug 2012 but also that I am not due an upgrade until May 2012. At no time was it ever discussed with me that this was a new contract and it certainly is not obvious from the peice of paper that I signed last year. Am I now stuck with this contract that nobody explained to me!!?!