Car Track debits my account without my consent

I cancelled 2 accounts after I had sold 2 of my vehicles. The contract stipulated that in the event of a cancellation I pay R2500 per vehicle. I spoke to a CarTrack service agent with whom we agreed that I would pay the amount (R5000) over 3 months in equal instalments. My account had been in arrears for 1 month, and the total came to R6000. Per month I was to pay R2100 over a period of 3 months. Car Track then deducted R2100, R2000, R570, and R25 in the same month of July. I phoned to reverse the ******* transactions and Car Track is saying they are not paying me back since I owe them.