HiFi Corp Laptops Repair Complaint

Please assist. I bought an Acer laptop at HiFi Corp in August 2018 which was on sale. Upon buying it I was told to keep the Invoice safely as the laptop is under warranty for technical issues- the guy even made an example and said, "such as lines appearing on the screen." In October, just 2 months after purchase, as I was opening the laptop and adjusting the screen so i can see properly, horizontal lines appeared on the side of the screen. this is a personal laptop and i travel daily on public transport with my work laptop. I went to HiFi Corp in festival, was advised that this will be fixed as it is part of the warranty and the laptop was booked in repair without a single dent or scratch. I've now been called to be told that the lines appearing on a screen that i brought back to store with no dent or scratch, is my fault, and it no longer falls within warranty. I don't understand how i am blamed for lines appearing on my screen in only 2 months after purchase. I am very disappointed in the treatment i have received from your festival mall, kempton park store by your sales manager Tendai Mtasa over the phone. Again, to be held liable for the repair of that laptop i was sold and is now showing lines in only 2 months. I'm being ******* with IT terms, because yes i don't understand such, I'm a finance professional. I was told the laptop is covered for technical issues such as lines on the screen, suddenly the lines are my fault, and certain lines are suddenly not classified as technical? With no scratch or sign of impact to the laptop. the lady that booked it for repair even said if it was ink on the screen we wouldnt even bother booking the thing into repair. It raises question to the quality of electronics that are put on "SALE" at the stores. Please advise me on this matter, because i refuse to pay over R2000 for them to now repair my screen. Acer as the manufacturer and HiFi Corp as the merchant, I am highly disappointed and will not be held liable, I only wonder if the qaulity of the laptop is the reason they put it on sale. I can even recognise the lady at Customer care that said, alot of laptops have been returned due to issues, why must i as the consumer be held liable, unfairly so by big merchants because we seen as just "minor" consumers.