MTN won’t cancel my contract

For the past five months ive been trying to cancel my contract with MTN, they tell me that its been cancelled they even give me a ref number. However month end comes, and the debit order goes from the bank, when i dispute it, they block my number from dialing out, data and sms... when i go to the branches they tell me that it appears that i still have a contract, and i have to call the retention dept. im so dissapointed as this means i have to be on hold for about 15-30minutes for the retentions and repeat the process... only to have them debit me again