Canceled contract

I returned the laptop that was delivered to me in March, to one of the MTN Shop in Southgate after querying the false advertising of the promotion they had in that particular month. This was done after the consent between Mondo and myself, that I return the laptop and that it will be canceled on their system and no debit orders will be initiated. To my surprise the debit order for +/-R1800 went out in March and again in April (25) after I had spoken to them. The laptop was returned to MTN but I still get charged.....I really don’t know what to say anymore.. been going back and forth with this query and still seems like it hasn’t been resolved, I got an SMS saying MTN is debiting me +/-R1800. I can’t be charged for something that is not in my possession. I need these extra R429 reversed for two months and cancel them completely. I am really not happy with your service, after so many calls to Mondo Mtn with different consultants I have been talking to. Reference number: RC*** and IRMS***.