Bad Service From Tracker Faulty Tracking Device

On 13 August 2019 Tracker advised me via SMS that their tracking device that was fitted to my car had malfunctioned and needed to be replaced. If the device was less than 3 years old I would be liable for replacement cost. I telephoned Tracker to inform them that I wished to cancel the contract since they were not providing the service contracted for i.e. non-performance on their behalf. The agent stated that the contract had already exceeded the 36 month contract period and they would fit a new device subject to a new 36 month period. That contract was not concluded for reasons Tracker is fully aware. On 15 August 2019 Tracker debited my bank account, since Tracker admitted that the contract had expired, plus their device was faulty and they thus did not render any services I instructed my bank to reverse the debit order payment. On 15 September 2019 Tracker again debited my bank account ~ again I reversed the payment with instruction debit order not authorised. On 17 September 2019 Tracker advised me per SMS to remedy the debit order of 15 September or call their credit controllers. I made 5 FIVE phone calls to Tracker in this regard but the only response was an automated prompt to hold on since they were busy. For four of the calls I held on for more than six minutes but on one picked up the calls. The next day I called again and held on for more than 1 minute. On 18 September 2019 Tracker emailed me a letter of 30 Day Demand for Payment. I sent them 3 emails but have not received the courtesy of a reply. Needless to say Tracker had threatened to have me blacklisted at credit bureaux but they fail to make any attempt to resolve the issue. They refuse to acknowledge my emails and simply fail to reply to my emails. This is totally unacceptable