Disappointed customer

I am a truly disappointed customer in the service being done to fix my garmin nuvi 52 navigation device. I bought the device last year around August 2014 by HiFi corporation by Menlyn mall in Pretoria and I even paid an extra R400 for an extra 3 year warranty. Now when I took my device in January 2015 on the 6th to Hifi Corporation a lady by the name of Petunia received the device for repairs by customer service and printed a slip for me and took it for repairs by the supplier (in this case I would think Garmin). I was only told at the end of February 2015 after the six weeks of working days had exceeded that the device has some liquid in it and is not covered by the warranty, the cost to repair would be R850. I told HiFi corporartion by Menlyn this is fine, I will not be repairing the device then, they should bring the device back. I have been begging HiFi corporation to bring the device back, even contemplating why I was then told the R400 I am paying for an extra warranty does not cover fixing the device. It is now the 4th of May 2015 I have been calling weekly asking about my device but still no response as to what is exactly happening. Job number: 6299