I'm so disappointed and Hurt ... I really need help

I'm taking this matter further now after I have waited for so long without any feedback from the store manager. He promised to speed up the process and give me feedback but I have to call him always. this is what happened:

bought a second hand television on Saturday (18/01/20) afternoon, and they switched it on to show me it was working, then switched it off again. when got to my place I switched it on and selected the channels, i watched it for not more than 10 minutes then it switched off, tried switching it on but it didn't switch back on. because I didn't have transport to take it back and it was a bit late, I took it back to the shop the following day (18/01/20), I told them what happened and that its either they give me another TV or they refund me. the staff was very rude, instead of helping me or coming up with the solution, they kept on coming up with excuses that the TV was working before leaving the store, so its not their fault, I mean like they said it has a 6 months warranty, now they cant assist me because the TV was working before. i asked them to call the manager, the manager was nowhere to be found, they said they'll call me the next day (20/01/20), I had to call them and asked to speak to the manager, he was also rude, He also mentioned that its not his fault he still needs to take the TV to the technicians, then i asked him when is he going to get back to me, he said he doesn't, not this week, not next week and not even the third week. I'm so disappointed and I don't think I'll buy anything from them again. I really need my money back

the store is located at Benoni Lakeside Mall, and I really need help because now they have my money with them and I don have a TV. its so sad how these stores are treating their customers, especially loyal customers. :(