Harassed and abused by Cartrack

I would like to express my disappointment in how Cartrack treats its ex clients if I could put it that way, I used to have a tracking device with car track and unfortunately due to unforeseen circumstances I had to get rid of the car and have made payment arrangements with Cartrack to settle my outstanding balance, however I keep getting emails and phone calls from Cartrack threatening to blacklist me if I don't settle the account even after there is a payment arrangement in place and they have been debiting me for the past 7 or 8 months now, I am really tired of these emails and will now seek legal advise regarding this as I have tried on several occasions to address this and seems like my concerns are falling on deaf ears. Can CARTRACK PLEASE STOP HARASSING ME as I have come to the party and paying my account every month as per our agreement/arrangement.