contract never cancelled after 8 months of trying

I have cancelled a contract with vodacom in november last year , after paying it up, only to find out this year that cancellation was never done, two months ago i called vodacom to cancel the line for me and i was assured that its done, today i was shocked to notice that my 5 gig data wifi was not opening s i call them to verify if they loaded my data, they said its because my account is in arrears and that iam owing them R600 , cause the other contract was never cancelled,iam tired with vodacom , trust me i need legal advise on how to terminate their stupid contracts in court and sue their ass off , i dont want to hear or see them anymore, the stupid consultant who was assisting me told me he logged a call and the matter will be resolved in 7 days , can you believe that nonesense?