Taking money out of my account

I’ve had the worst service with Cartrack. I called them to notify them that I’ll be selling my vehicle and would like to cancel the contract but id like to request a payment arrangement to pay the amount over 3 months. I was then transferred to the accounts department in which the payment arrangements was made and the first payment would have started on the 25th of September 2026. The amounts were also sent and I approved the Debi check for the 3 amounts. After I had already paid my instalment for the month and also the notice period would have ended on the 22 September 2026, they have debited my account with R850 this morning. I then called and was advised that there can be no payment arrangement on a cancellation fee. I then asked why the full amount was not debited then since it was a 1500 and some rands. The lady then said I approved the Debi check so they are allowed to take that amount. However the Debi check I approved was not for an amount of R850 and the notice period is only currently on 2 days. Cartrack is the worst company to have a tracking device at honestly.