Bad Service

I need help, i receive phone call everyday from cartrack telling me the one thing saying i must pay my arrears of plus/minus R9000.00 which i dont agree with the amount. i tried to prove myself that im over charged and somewhere somehow cartrack legal department noticed that and was told that they will re check their system but instead they dont do that, what they do is to phone me everyday harrassing me that i owe them 9k. i tried to request the detailed statement why am i owing them 9k but they are failing to do that. and there was a time where they just decided to deduct 3k from my account without my permission. i dont owe Cartrack 9k. and what was told is that i owe them for two cars which is **** ****. yesterday i got a message with a heading of BLACKLISTING IMMINENT: i must pay R8300 within 20 days or otherwise wil be blacklisted. i felt so harrassed cause was told that they wil go and re-check their system but now it seems like they not taking me seriously. i have a proof to show that i only owe a 1car not 2cars. i even requested a contract but they failed to provide me with a contract. i started to reverse debit orders after realising that im now owing them a lot of money which was a false amount. please help before i report them further. and even the premium was increased without my knowledge.