Mix Telematics communication skills

My Father was called by Mix Telematics to use their tracker services. My Father agreed and advised them that he is 1 with auto trader. The salesperson advised my father that he must not worry, it will be cancelled for him. NOW, AUTOTRADER'S ATTORNEYS are calling my father demanding payment.

I want to know who is liable for the AUTO TRADER demand?

I have been calling Mix Telematics and the service is pathetic and Ive been transferred too many times.

if there is proof that Mix did advise auto trader that they must cancel. sent us proof.