Cancellation policy not in terms and conditions

My24 mth contract period ended. I paid last months instalment and was told at the store that I will still have a bill next month as I need to cancel the contract and go onto prepaid and in addition if I do not cancel the contract then I will still be billed monthly subscription. I asked for the original contract and nowhere on my contract is it stated that I have to cancel a month before the end of my 24mth contract period. I asked for terms and conditions and it is not listed here either. I called the customer care centre and they tell me that it is in the terms and conditions, the lady at the store also stated that she informs her clients and writes on the copy of contract, \qualifies for upgrade 3 months before end of contract and cancel 1 month before contract end"as she has had lots of queries from unhappy customers. I am unhappy that this was not pointed out to me at the beginning of the contract period"