vodacom broke my phone

About two months back, my wifes ' so called' waterproof sony got splashed with water in the shower and stopped working, after being booked in with vodacom for assessment it was returned stating that it was water damaged and would not be repaired under warranty, i re-booked it in for a second evaluation and the same result was obtained. I was informed of this and went into the store to collect my ' damaged phone ' to my astonishment the back cover was cracked from left to right , i was irate and refused to take a now ' broken broken' phone out of the store and had asked the manager to replace the broken part. by the way the phone was in working order and was operating normally as if nothing was damaged, a technician at the repair center mentioned to me the the cable connecting the screen to the phone was corroded, nevertheless the phone worked fine, some corrosion !!! . its about two months gone by i still have no phone and have to pay 399 pm for a phone that was only 4 days old when all this trouble happened, vodacom has to investigate the source of the breakage on my phone. why should i have to suffer while vodacom investigates can they not just replace my back cover