mtn doesn't want to terminate my contract, despite it ending 6 months ago

my mtn contract was due for cancellation on the 18 April 2019 ,I phoned customer care before the due date to inform them that i wont be upgrading,and requested that my account be de activated, but to date no cancellation has been made I have contacted them countless times with the same request but all they do is keep charging me,i ended up paying for the charges because they rated me as a bad payer.the last time I phoned them, they promised to pay me back all the charges incurred because according to their records I don't owe them anything its them that owe me since I requested for no upgrade and the fault is on their side,but to this date no action has been taken and the contract is still active,I cannot believe mtn is doing this after I honoured all my monthly payments. At this point I don't have any energy left to call the mtn customer care centre and emailing them,I just hope I get help here at hellopeter.