Netstar decides to install a new tracking device without my consent

I purchased a new vehicle which the dealer decided to add a Netstar installation without my permisssion. However I cancelled this with them before taking delivery and installed another tracking device when I collected the car. Now all of a sudden I receive an invoice from Netstar for this monthly amount. After sitting on their phone lines for over 40 mins to cancel, I was told they had my consent to have this installed through the dealer. They did not have my consent, until such time that they can prove that I requested this service. Netstar claim that my consent is given through the dealership. I asked then what stops anyone saying go and install a unit in another car without the owner's written or verbal consent? They now want me to pay their invoice for this period plus another 20 days and that I need to escalate this to the dealer, which I have but I will not be paying for any invoice until they can show me that I gave any form of consent either verbal or written for them to install this device.