Poor Ridiculous service

Cartrack consultants and services is the worst ever, I'm very unhappy with how they handle matters. I cancelled my contract with them which I had to pay a cancelation fee, I did pay went on and opened a new contract and ffor some ridiculous nonsense I'm being told my account is in errors, iv sent several mails and explained with proof of payment to no assistance now I'm being threatened with a letter of demand, they so quick to jump to nonsense