Defective products

I purchased a Sony Xperia Z3 Compact on an upgrade contract through Vodacome 4U on Saturday 14 Feb 2015. On Monday 16 Feb 2015, after having the phone for just 2 days, the whole back glass \splintered"in my hand while I was walking. The phone has never been dropped by me (only had the dam thing for 2 days). I immediately took the phone back to Vodacom 4U (note within 7 days of purchase) and they told me that they needed to send it to Sony to be assessed. Today I get a call telling me that I need to pay for the repairs on the phone. Unacceptable. The phone was not damaged due to my negligence. I have subsequently been onto countless forums and have seen that ghost cracking of both the back and front glass of this phone is a very common problem and often happens when the phone is simply lying on a table or being charged and Sony continues to deny that there is a design default. This is unacceptable and I am very unhappy with Sony and the service / attitude of both Vodacom 4U and Sony. I am told either to take back the defective product or pay for the repairs out of my own pocket. Vodacom 4U was very quick to \""wash their hands\"" of the matter so they could get their loan phone back. """