Irritated and fed up with TELKOM

I app**** in June 2018 for a mobile wifi contract with Telkom, my first question to them was is there coverage in my area and they agreed. I received the mobile device and tried to activate, but was contacted by Telkom 2/3 days after to advise me that there is no coverage in my area, which was disappointing. They then advised me that I must return the device and they arranged a courier to collect everything which I received from them. The contract was for R139.00 a month and they deducted the debit order as agreed for that month and I has to reverse it. I have been struggling ever since then to stop them from deducting the debit order from my bank account and it's 10 months later now. Every month the debit order gets more because I have to go and reverse it every time it goes off my account. I've even considered to change my bank account, but then I received a sms from a debt collection service stating that I might be blacklisted if I don't settle the account. I phoned Telkom call centre and explained my situation and got reference number, I sent email to Telkom to try and resolve this and I even went to a Telkom store in Knysna to see if they can assist and I was told that my query will be sorted and again received a reference number. I am now very irritated and fed up with this type of service received from such a big company and I don't know what to do in order to sort this out. I can change my bank details, but I don't want a bad credit record, so I'm therefore in a very difficult situation. TELKOM CLOSE THIS ACCOUNT.