Bad service. I want my money back

I bought a TV at HOUSE & HOME at Hanstrydom street in Pretoria. Then three month after the purchase the screen started to shrink. I phoned them then they said I must bring it to the shop they will try to fix it. Then after three weeks they phone and they said they can't fix or replace it claiming that I broke it myself. They can't do anything now I feel like I lost my money. The guarantee is 1 year and I also have proof. I want my money back they can keep their TV. I bought cash.