Vodacom

I toók out a contract phone with Vodacom,I paid the full 2yr contract, when the contract,, in my opinion,ended they continued deducting for the phone,upón enquiry í was told that I had to call vodàcom cançel, by this time I was in arrears oñ the account,I paid to what was owed and now I'm having difficulty canceling the contràct after numeróus attempts,i have also a now tarnished credit score àfter keeping my credit score unblemished,please help me on this