One Car... Two Premiums

I bought a new car mid-August and traded in my old car. Both vehicles ha/have Trackers installed. I made sure to timely cancel the subscription to Tracker for the old vehicle which I traded in. The new vehicle's tracker was then also activated. The call centre ensured me that only the premium for the new vehicle would go off at the end of August 2017. i asked for an email to confirm this in writing. None was received. On 1 September I saw that double the premium was deducted. This is unacceptable. The same happened to my father and to speak to someone at your call centre is like talking to a wall. I immediately reversed the debit order. I suggest someone contacts me to rectify this problem, so that I may pay ONE premium for the new car, so that my Tracker is indeed activated this month.