Sony Mobile - Not repaired under warranty

My device was repaired * times and * motherboards were replaced within * months. I submitted the device to the service centre for the *th time on ** april and collected the same on **th may ****. Within * or * days of repair, i noticed the front camera showing a black screen or gets stuck when opened and sometimes it worked, which i thought was a software issue. I couldn't arrange the time to visit the service center again as they already wasted my enough time and money (travel expenses) plus my internship was already in process. After nearly two months, my device switched off automatically and never turned on, neither it was charging. Now i had to submit the device in service centre for the *th time and i mentioned the camera issue too, after opening the device and they showed me the camera wire has a little cut in the middle, and told me that the camera will not be considered in the warranty and asked to pay it. I don't understand why should i pay for it, when it's done by the repairer.
P.S. I took pictures of the device before submitting to the service centre. The pictures clearly show that the device doesn't have any indication of being dropped or being opened or any abuse.
Job no. W************