Disatisfaction with Vodacom

I took my BRAND new Xperia in to Vodacom due to SD card error and later on the phone just randomly rebooted.Took it in the Wed, got it back the Thurs as repaired. Had to take it back the Friday cause it was still doing the same.Now 2 weeks later i am slapped with a quote for R1200, although the phone is still under warranty. They claim its for physical damage to the device on the inside! How in heavens name do i even get to the inside of the device?When i booked in the device, there was no damage to the outside of the unit.For me to gain access to the inside, there would have been marks to indicate that on the outside. Now its a whole issue cause they expect me to pay the R1200, cause the claim the warranty is voided due to the physical damage. What load of ... Now its been escalated but no one can tell me exactly what the holdup is.