Failure to attend to double billing

My private Home Telkom account was double billed from June 2017 until July 2018. The double billing originated from a failure of Telkom to cancel a service which I upgraded from. Essentially being billed for my current service and a service which was supposed to be cancelled. I reported this matter and was assured it would be attended to within 14 working days. This did not occur. I then followed up the matter and upon which the matter was escalated. I was then assured that the matter would resolve within 72 hours. I queried further a week later and the matter still had not been attended to. This isn't even a lack of service delivery, it is taking of money for a service that isn't even supposed to be provided. A passive approach through the correct channels and protocols has yielded no results. A very poor display from the accounts department and management.