Blacklisted threatening SMS's

<div>Good day, received an SMS from cartrack today advised that if i don't pay the outstanding amount within 15 days i will be black listed, this even through i have a payment arrangement in place. This after send a mail to cartrack requesting proof of services that provided to me as a customers and yet that cannot be done either. How can some be blacklisted even if they have payment arrangements in place? I will never advise anyone to ever do business with cartrack. Pathetic service delivery, had a unit in my car, as soon as the battery is disconnected they call you, say you are shot, and cant answer your phone, no service after that call no response attending absolutely nothing</div>