misleading selling

i bought a contract phone in around 2014/03/31. it was a years contract according to my understanding. I paid up and late they told me i have to give notification 30 prior which was not disclose at sale initiation. well paid and place the notice, when that notice time reached a consultant from vodacom called me telling me i was a good customer and offer me either an upgrade or airtime contract i refused. later the continue loading airtime again i called asking them to reverse they told me its impossible i had to pay the account which has way passed it term (24 months). i asked for the settlement letter emphasizing that i don't want anything to do with them or the contract. the provided the settlement letter, but now they say i am owing and listed me on credit ITC as bad debts while i have paid up letter with me.