Unhappy client

I cancelled the cartrack service last year November, they deactivated their tracker and kept on billing me. When i call to enquire they said the tracker was still on their side even though it was off on my side which i dont understand until today how does that happen but they finally cancelled n send me a message in May 31 stating that i owe them R1625 n they are offering me 40% off over 2 months meaning R488 per month over the 2 months. I made arrangements there after i paid R488 on the 9th of June and on the 20th they debited R498 which i assume the R10 is for the debit order, my balance was suppose to Zero. But I'm still receiving messages stating I'm owing R648.74 which i don't know for what it is now. I tried to call me they kept on saying they will check and call me back. I curse the day i signed up with Cartrack.