Mix tellematics debit for no unit

So i contacted Matrix tracking to install a new unit into my newly purchased vehicle as i cancelled the month to month unit in my old car. Arrangements was made for the installation team to contact me the next day to arrange a time and date. They then phoned me 2 days later to arrange a time and day and told them if they cant even confirm and stick to a set turn around time they must better cancel the installation as i am no longer interested. Well well well.... i get a debit order month end from Mix Tellematics for a unit that was never installed. I called them to query it and got told they will resolve the issue. Then i get threatening mails and sms notifications that if i do not pay the amount i will be listed with the credit bureau. Shows you how useless they are if they cant even resolve this issue