Whose fault is it?!

I checked my Huawei P8 lite cellphone during Jan '16 to find out why I couldn't delete unsent sms's and why internet browsing was slow. Eastgate Customer Centre couldn't sort out problem so they sent it to head office Advanced Repair Centre. Report back was liquid indicator was activated, could not say how or when it happened but wanted R1994,20 to replace device because warranty did not cover & they don't repair. Unwilling to cancel contract which was upgraded end Nov 2015 or waive fee for a 1 and a half month new phone protected by cushioned cover and never fell/exposed to liquid onmy side. How does one prove whether damage pre-existed before I took delivery or damage at Vodacom's hands when phone checked in. Advanced Repair Centre glibly returned phone to Eastgate who in turn shrugged shoulders as a \nothing can do\" when I went there yesterday 2/2/16. They then discovered I was insured when I queried so phone is going to be replaced. Question is: when do such giants acknowledge liability for defective products without passing on the buck?"