Poor service - Telkom Mobile.

I have cancelled my Telkom Mobile data contract with Telkom Mobile from the 1 June 2019. Till this date I am still receiving an invoice from them and moreover I was over debited on my personal account. I have been in constant contact with them. Their call center agents have no clue about their own procedures regarding refunds. One says its 24 to 72 hrs and indicated that I will receive my refund this week (call logged on 1 Aug 2019) and another says 24 to 72 working hours for someone to be allocated to my case and thereafter another 2 to 7 working days for an outcome. Not even a refund by then. They must then still contact me to refund my account. A whole month can go by for them to refund me for their own mistake. But yet when they do not receive the debit order that meant to come off my account then I need to pay penalty fees for failed debit orders. Yet I do not receive anything more for them keeping money that does not belong to them. I should be entitled to interest for the money they are holding. No because of their mistake, I need to now pay penalty fees for other failed debit orders by my other debtors. This is not fair. Telkom mobile is the most useless telecoms service provider in SA. I would really not encourage anyone to use Telkom mobile. They are useless and inconsiderate.