Extremely poor service

We bought a 75" flat screen tv from them and now 7 months later the tv packed up, when you switch the TV on you just get a black screen. We called HI-FI Corp Kempton Park which is where we bought it. They told us to send a mail with our details and then they will log a call for a Technician. Which we did, we then call to find out if the mail was received and we were told that Cansandra is not even at work. We were advised that we spoke to Aiyanda, they put us through to her, when I chatted to her she send asked us to send the serial number, why she didnt say to send it in the email in the first place is beyond me. Then I asked how long would it take and she told be between 7-21 days for the technician to come out and fix it. Really??? My goodness now thats service for a TV that nearly R20000. Now I know why they try to sell you extended warranty. This is really bad and such poor service.