Bad Client Service

I have a Vehicle tracker installed by Mix telematics, I noted that the tracker is dysfunctional, reported it and was informed that someone is gonna come to check it but never came despite several reminders but instead continued to deduct premiums for the service they are not providing until I decided to reverse these premiums because I could not continue paying for a disfunctional tracker. I also wrote to them to cancel the contract, but after all these attempts the company handed me over to credit bureau, when I contact them the phone just rings without being responded to, and I wrote an email, I got a reference no.back and was told that someone is going to revert back to me but to date the company has not contacted me, no response to email when I follow up by email, no response to telephone calls, now I am stuck with a bad credit record of which they are the only ones to remove that.