Telkom mobile Cellphone contract warranty problem

I took out a contract with Telkom mobile in July 2019. I've been using the headset since then. My screen just went black, calls come through, but the screen is black. I took it back for fixing as it was still under warranty. Unfortunately they called me to say they can't fix the phone because it was physically damaged, and therefore it voids the warranty. They said the cost of fixing the phone will be R5449. that they said I must pay. I said I don't have that amount. They did not even explain what physical damage it was. Instead I was told that in order to get my phone back I must pay R189. for the assessment of the phone. I am now paying a contract of a phone that I'm not using. They further said should I take it to be fixed elsewhere, they will never and I experience problems, the warranty of the phone won't cover me anymore. Please help