MATRIX TRACKING DEVICE NOT ADHERING TO MY CANCELLATION REQUEST.

I have recently cancelled my account with matric tracking in December,wrote them an email about my cancellation and kept on doing follow ups on that with emails and thereafter they have been taking money from account without my permission.i have got calls from them asking me to pay each and every month and now the money is becoming a lot now,today I got a message from them saying that I must pay to avoid credit bureau listing meanwhile they have been calling me and dropping their calls on my ear whenever i speak to a consultant that I have cancelled my account which is very rude I even sent them an email about it but I’m still getting such messages.Can someone please assist me with that please because I’m a loyal client and I’d like to keep my credit score clean.