Repair quote keeps increasing

My company upgraded our cellphone packages and I received a Sony Xperia Z3 in December 2014. I worked with the phone for approximately two months when I started having problems when the phone would keep updating and freezing. I informed head office and I had to get the phone to them. Borrowing another phone, I went to Vodacom to transfer my info. I spoke to the tech assistant, he looked at the phone and told me it had a hairline fracture. This was hardly visible and could only be seen by tilting the phone, he also said this was a problem in some Xperia's as the phone gets too hot. I then put the phone back in the box and sent it to head office. The phone was given to Vodacom and a quote was received for +/- R2000, stating that the phone was dropped and needed repair. This was unacceptable as I had never dropped the phone. The phone was returned to me. I took it to Vodacom in Lakeside mall for a quote and the cost has now even increased to +/- R2500 and once again it was said that the phone had been dropped. How can a dropped phone have a hairline fracture, hardly visible but now need all these extra repairs? Out of almost 1 year, I used it 2 months, what about the warranty?