Complaint about car tracker

I've been paying car tracker since I bought my car in 2017, 4 mnts back they sent me a sms saying the device is faulty, i foned them, they said i must pay R600 for re installation, i asked why must I pay R600 if their device is faulty they must change it for free like other companies, eg the one that I joined now, I requested to cancel the contract with them and asked them not to deduct my money they agreed, but mnthend they deducted my money, I went and reverse it, yesterday I received a message from their lawyers that am owing R441, they will send the payment request to my company, I told them that my company won't allow it, today I received another sms from car tracker saying if I do not pay R441 within 20 days they going to blacklist me, really, from my point of view if someone doesn't pay insurance for 3 mnts or reverse the money, that company, cancels the policy, u can't say u owing 3 mnts we blacklisting you, so is this the way the companies are treating people, I've never claimed anything from this company all these monies that I've been paying r they not enough with it, that they want to blacklist me, dd I borrow money from them, I'll fight till the end, but I've already reported to my lawyers