Poor level of service

I am really not happy with Telkom stores, there customer service is pathetic and appalling. I am an existing customer with Telkom and I decided to take out a new contract with them for an an iPhone 6S at a telkom store in Kenilworth Centre as I was taking it for my brother which was on Wednesday the 6/2/2019.When I arrived home, I realised its not the phone that it's not the phone he wants, he wants an iPhone 7 or 7 plus. I therefore went to the store in Bayside the previous day as I was working and explained the issue to them and they said that I should go back to Kenilworth and they should exchange it. So today the 10/02/19,I decided to go and exchange the device as I spoke with shameega their acting manager on duty, so that I can get the iPhone 7 or plus as I am willing to pay for the iPhone 7 contract. They refused to take the device and said they can't exchange it. Even if the phone has not been used. I am really not happy with Telkom and their service. Their service is appalling, I am even thinking of ending the existing the contract that I have with them even if it's due for an upgrade. They don't know how to keep their existing customers.