unauthorised billing

My contract with MTN ended on the 17thJanuary 2016. On the 14th I contacted 808 again to ascertain if that is the process and I was advised that I can do it on the 15th Jan plus I can only convert my contract to prepaid on that day. I was advised to sent an e-mail to retentions to advise about the convertion to prepaid which I did. A few days after I was contacted by someone from their head office to advise me that I can rather look at other alternative contracts and I then went to the store to look at the options. I was advise by the store at Mafikeng Mall in Mafikeng that they ran short of mini-ipads , I was then given a form which will be used for the follow up as soon as the mini I-pads are available. On Saturday I realised I was credited with my initial contract's data and airtime and that is when I contacted 808 today. I was advised that I did not inform MTN to cancel the contract and will be liable to pay the monthly subscription fee that I have been pay. I am highly disappointed and have more reasons why I should completely shut MTN from my dealings. I need this matter resolved asap and don't mind even if you can reverse your data and airtime , I don't need it.