Failed To deduct agreed amount

Cartrack is full of nonsense, I took a premium of R170 and they sold me a tag that would add to an amount of R250 that I was supposed to pay monthly yet they have been deducting R170 concluding the tag was not added. 8 months later they give me a call saying that I owe them R1100 for the tag that they hate not been deducting from since I took the premium. Now they are threatening me that I will be blacklisted. Now whose fault is it that they have been deducting R170 instead of R250 from the get go?? They failed to do their job now they want to shift the blame to me . Their agents are not helping with anything instead they are rude and they don’t want to listen to what I’m saying. I do not recommend Cartrack at all,you will regret it. Take the cover at your own risk . customer service is zero