Billing not stopped after cancellation despite calls to tracker every month

I cancelled my tracker in August 2017. Tracker is still billing me for a service called agility . I have been calling them every month but to no avail. I keep reversing the debit order at my bank every month. This is becoming costly in terms of time and money spent every month to reverse this debit order. This month (January 2018) they have trebled the charge to recover the debit orders i have previously cancelled On 26 October i got the following email from them:

Good day

Thank you for the enquiry.

The Tracker Agility policy was cancelled as requested however due to a technical error your account was billed. We have requested a refund for the additional funds taken and it will reflect in your account in the next 7 - 10 working days. I can ensure you that this is not the way that we conduct business, we have notified our technicians and we are working on a way to prevent such incidents.

We would like to sincerely apologise for any inconvenience caused.

Please advise should you need any further assistance.