Telkom ruining my life!!!!!

I ordered a contract phone over the phone with Telkom. First of all the lady who was helping me with the phone **** about its quality and how good the phone is. When the phone got delivered I didn't like it immediately. And over the phone I was told that I could return it within 7 days I returned it within 2. The phone was collected from me by a courier company and returned to Telkom in time. I followed all procedure and cancelled the phone contract over the phone with various consultants. 5 months later Telkom debited almost R5000 from my account and they handed me over. This has greatly affected my credit score and I am in a process of buying a house. Someone didn't finish their job at Telkom and I'm greatly affected by this 💔💔💔💔. How best can I deal with this situation?